Block Tridiagonal Matrices in Electronic Structure Calculations
DEFF Research Database (Denmark)
Petersen, Dan Erik
This thesis focuses on some of the numerical aspects of the treatment of the electronic structure problem, in particular that of determining the ground state electronic density for the non–equilibrium Green’s function formulation of two–probe systems and the calculation of transmission in the Lan...
Multigrid Methods in Electronic Structure Calculations
Briggs, E L; Bernholc, J
1996-01-01
We describe a set of techniques for performing large scale ab initio calculations using multigrid accelerations and a real-space grid as a basis. The multigrid methods provide effective convergence acceleration and preconditioning on all length scales, thereby permitting efficient calculations for ill-conditioned systems with long length scales or high energy cut-offs. We discuss specific implementations of multigrid and real-space algorithms for electronic structure calculations, including an efficient multigrid-accelerated solver for Kohn-Sham equations, compact yet accurate discretization schemes for the Kohn-Sham and Poisson equations, optimized pseudo\\-potentials for real-space calculations, efficacious computation of ionic forces, and a complex-wavefunction implementation for arbitrary sampling of the Brillioun zone. A particular strength of a real-space multigrid approach is its ready adaptability to massively parallel computer architectures, and we present an implementation for the Cray-T3D with essen...
Isogeometric analysis in electronic structure calculations
Cimrman, Robert; Kolman, Radek; Tůma, Miroslav; Vackář, Jiří
2016-01-01
In electronic structure calculations, various material properties can be obtained by means of computing the total energy of a system as well as derivatives of the total energy w.r.t. atomic positions. The derivatives, also known as Hellman-Feynman forces, require, because of practical computational reasons, the discretized charge density and wave functions having continuous second derivatives in the whole solution domain. We describe an application of isogeometric analysis (IGA), a spline modification of finite element method (FEM), to achieve the required continuity. The novelty of our approach is in employing the technique of B\\'ezier extraction to add the IGA capabilities to our FEM based code for ab-initio calculations of electronic states of non-periodic systems within the density-functional framework, built upon the open source finite element package SfePy. We compare FEM and IGA in benchmark problems and several numerical results are presented.
Electronic structure calculations on helical conducting polymers.
Ripoll, Juan D; Serna, Andrei; Guerra, Doris; Restrepo, Albeiro
2010-10-21
We present a study of the electronic structure and derived properties of polyfurane (PFu), polypyrrol (PPy), and polythiophene (PTh). Two spatial arrangements are considered: trans chain (tc-PFu, tc-PPy, tc-PTh) and cis α-helical (α-PFu, α-PPy, α-PTh). Even at the small sizes considered here, helical conformations appear to be stable. Band gaps of pure, undoped oligomers fall into the semiconductor range. Density of states (DOS) analysis suggest dense valence and conduction bands. Bond length alternation analysis predicts almost complete delocalization of the π clouds in all spatial arrangements. Doping with electron donors or electron-withdrawing impurities reduces all band gaps close to the metallic regime in addition to increasing the DOS for the valence and conduction bands.
Real-time feedback from iterative electronic structure calculations
Vaucher, Alain C; Reiher, Markus
2015-01-01
Real-time feedback from iterative electronic structure calculations requires to mediate between the inherently unpredictable execution times of the iterative algorithm employed and the necessity to provide data in fixed and short time intervals for real-time rendering. We introduce the concept of a mediator as a component able to deal with infrequent and unpredictable reference data to generate reliable feedback. In the context of real-time quantum chemistry, the mediator takes the form of a surrogate potential that has the same local shape as the first-principles potential and can be evaluated efficiently to deliver atomic forces as real-time feedback. The surrogate potential is updated continuously by electronic structure calculations and guarantees to provide a reliable response to the operator for any molecular structure. To demonstrate the application of iterative electronic structure methods in real-time reactivity exploration, we implement self-consistent semi-empirical methods as the data source and a...
Structural and electronic properties of perylene from first principles calculations.
Fedorov, I A; Zhuravlev, Y N; Berveno, V P
2013-03-07
The electronic structure of crystalline perylene has been investigated within the framework of density functional theory including van der Waals interactions. The computations of the lattice parameters and cohesive energy have good agreement with experimental values. We have also calculated the binding distance and energy of perylene dimers, using different schemes, which include van der Waals interactions.
Three real-space discretization techniques in electronic structure calculations
Torsti, T; Eirola, T; Enkovaara, J; Hakala, T; Havu, P; Havu, [No Value; Hoynalanmaa, T; Ignatius, J; Lyly, M; Makkonen, [No Value; Rantala, TT; Ruokolainen, J; Ruotsalainen, K; Rasanen, E; Saarikoski, H; Puska, MJ
2006-01-01
A characteristic feature of the state-of-the-art of real-space methods in electronic structure calculations is the diversity of the techniques used in the discretization of the relevant partial differential equations. In this context, the main approaches include finite-difference methods, various ty
Electronic structure calculations of ESR parameters of melanin units.
Batagin-Neto, Augusto; Bronze-Uhle, Erika Soares; Graeff, Carlos Frederico de Oliveira
2015-03-21
Melanins represent an important class of natural pigments present in plants and animals that are currently considered to be promising materials for applications in optic and electronic devices. Despite their interesting properties, some of the basic features of melanins are not satisfactorily understood, including the origin of their intrinsic paramagnetism. A number of experiments have been performed to investigate the electron spin resonance (ESR) response of melanin derivatives, but until now, there has been no consensus regarding the real structure of the paramagnetic centers involved. In this work, we have employed electronic structure calculations to evaluate the ESR parameters of distinct melanin monomers and dimers in order to identify the possible structures associated with unpaired spins in this biopolymer. The g-factors and hyperfine constants of the cationic, anionic and radicalar structures were investigated. The results confirm the existence of at least two distinct paramagnetic centers in melanin structure, identifying the chemical species associated with them and their roles in electrical conductivity.
Ab initio calculations of yttrium nitride: structural and electronic properties
Energy Technology Data Exchange (ETDEWEB)
Zerroug, S.; Ali Sahraoui, F. [Universite Ferhat Abbas, Laboratoire d' Optoelectronique et Composants, Departement de Physique, Setif (Algeria); Bouarissa, N. [King Khalid University, Department of Physics, Faculty of Science, P.O. Box 9004, Abha (Saudi Arabia)
2009-11-15
Using first principles total energy calculations within the full-potential linearized augmented plane wave method, we have studied the structural and electronic properties of yttrium nitride (YN) in the three phases, namely wurtzite, caesium chloride and rocksalt structures. The calculations are performed at zero and under hydrostatic pressure. In agreement with previous findings, it is found that the favored phase for YN is the rocksalt-like structure. We predict that at zero pressure YN in the rocksalt structure is a semiconductor with an indirect bandgap of 0.8 eV. A phase transition from a rocksalt to a caesium chloride structure is found to occur at {proportional_to}134 GPa. Besides, a transition from an indirect ({gamma}-X) bandgap semiconductor to a direct (X-X) one is predicted at pressure of {proportional_to}84 GPa. For the electron effective mass of rocksalt YN, these are the first results, to our knowledge. The information derived from the present study may be useful for the use of YN as an active layer in electronic devices such as diodes and transistors. (orig.)
Real-time feedback from iterative electronic structure calculations.
Vaucher, Alain C; Haag, Moritz P; Reiher, Markus
2016-04-05
Real-time feedback from iterative electronic structure calculations requires to mediate between the inherently unpredictable execution times of the iterative algorithm used and the necessity to provide data in fixed and short time intervals for real-time rendering. We introduce the concept of a mediator as a component able to deal with infrequent and unpredictable reference data to generate reliable feedback. In the context of real-time quantum chemistry, the mediator takes the form of a surrogate potential that has the same local shape as the first-principles potential and can be evaluated efficiently to deliver atomic forces as real-time feedback. The surrogate potential is updated continuously by electronic structure calculations and guarantees to provide a reliable response to the operator for any molecular structure. To demonstrate the application of iterative electronic structure methods in real-time reactivity exploration, we implement self-consistent semiempirical methods as the data source and apply the surrogate-potential mediator to deliver reliable real-time feedback.
Electronic Structure of Silicon Nanowires Matrix from Ab Initio Calculations.
Monastyrskii, Liubomyr S; Boyko, Yaroslav V; Sokolovskii, Bogdan S; Potashnyk, Vasylyna Ya
2016-12-01
An investigation of the model of porous silicon in the form of periodic set of silicon nanowires has been carried out. The electronic energy structure was studied using a first-principle band method-the method of pseudopotentials (ultrasoft potentials in the basis of plane waves) and linearized mode of the method of combined pseudopotentials. Due to the use of hybrid exchange-correlation potentials (B3LYP), the quantitative agreement of the calculated value of band gap in the bulk material with experimental data is achieved. The obtained results show that passivation of dangling bonds with hydrogen atoms leads to substantial transformation of electronic energy structure. At complete passivation of the dangling silicon bonds by hydrogen atoms, the band gap value takes the magnitude which substantially exceeds that for bulk silicon. The incomplete passivation gives rise to opposite effect when the band gap value decreases down the semimetallic range.
Efficient Execution of Electronic Structure Calculations on SMP Clusters
Energy Technology Data Exchange (ETDEWEB)
Ustemirov, Nurzhan [Iowa State Univ., Ames, IA (United States)
2006-01-01
Applications augmented with adaptive capabilities are becoming common in parallel computing environments. For large-scale scientific applications, dynamic adjustments to a computationally-intensive part may lead to a large pay-off in facilitating efficient execution of the entire application while aiming at avoiding resource contention. Application-specific knowledge, often best revealed during the run-time, is required to initiate and time these adjustments. In particular, General Atomic and Molecular Electronic Structure System (GAMESS) is a program for ab initio quantum chemistry that places significant demands on the high-performance computing platforms. Certain electronic structure calculations are characterized by high consumption of a particular resource, such as CPU, main memory, or disk I/O. This may lead to resource contention among concurrent GAMESS jobs and other programs in the dynamically changing environment. Thus, it is desirable to improve GAMESS calculations by means of dynamic adaptations. In this thesis, we show how an application- or algorithm-specific knowledge may play a significant role in achieving this goal. The choice of implementation is facilitated by a module-driven middleware easily integrated with GAMESS that assesses resource consumption and invokes GAMESS adaptations to the system environment. We show that the throughput of GAMESS jobs may be improved greatly as a result of such adaptations.
Electronic structure calculations toward new potentially AChE inhibitors
de Paula, A. A. N.; Martins, J. B. L.; Gargano, R.; dos Santos, M. L.; Romeiro, L. A. S.
2007-10-01
The main purpose of this study was the use of natural non-isoprenoid phenolic lipid of cashew nut shell liquid from Anacardium occidentale as lead material for generating new potentially candidates of acetylcholinesterase inhibitors. Therefore, we studied the electronic structure of 15 molecules derivatives from the cardanol using the following groups: methyl, acetyl, N, N-dimethylcarbamoyl, N, N-dimethylamine, N, N-diethylamine, piperidine, pyrrolidine, and N-benzylamine. The calculations were performed at RHF level using 6-31G, 6-31G(d), 6-31+G(d) and 6-311G(d,p) basis functions. Among the proposed compounds we found that the structures with substitution by acetyl, N, N-dimethylcarbamoyl, N, N-dimethylamine, and pyrrolidine groups were better correlated to rivastigmine indicating possible activity.
Gradient type optimization methods for electronic structure calculations
Zhang, Xin; Wen, Zaiwen; Zhou, Aihui
2013-01-01
The density functional theory (DFT) in electronic structure calculations can be formulated as either a nonlinear eigenvalue or direct minimization problem. The most widely used approach for solving the former is the so-called self-consistent field (SCF) iteration. A common observation is that the convergence of SCF is not clear theoretically while approaches with convergence guarantee for solving the latter are often not competitive to SCF numerically. In this paper, we study gradient type methods for solving the direct minimization problem by constructing new iterations along the gradient on the Stiefel manifold. Global convergence (i.e., convergence to a stationary point from any initial solution) as well as local convergence rate follows from the standard theory for optimization on manifold directly. A major computational advantage is that the computation of linear eigenvalue problems is no longer needed. The main costs of our approaches arise from the assembling of the total energy functional and its grad...
Adaptations in Electronic Structure Calculations in Heterogeneous Environments
Energy Technology Data Exchange (ETDEWEB)
Talamudupula, Sai [Iowa State Univ., Ames, IA (United States)
2011-01-01
Modern quantum chemistry deals with electronic structure calculations of unprecedented complexity and accuracy. They demand full power of high-performance computing and must be in tune with the given architecture for superior e ciency. To make such applications resourceaware, it is desirable to enable their static and dynamic adaptations using some external software (middleware), which may monitor both system availability and application needs, rather than mix science with system-related calls inside the application. The present work investigates scienti c application interlinking with middleware based on the example of the computational chemistry package GAMESS and middleware NICAN. The existing synchronous model is limited by the possible delays due to the middleware processing time under the sustainable runtime system conditions. Proposed asynchronous and hybrid models aim at overcoming this limitation. When linked with NICAN, the fragment molecular orbital (FMO) method is capable of adapting statically and dynamically its fragment scheduling policy based on the computing platform conditions. Signi cant execution time and throughput gains have been obtained due to such static adaptations when the compute nodes have very di erent core counts. Dynamic adaptations are based on the main memory availability at run time. NICAN prompts FMO to postpone scheduling certain fragments, if there is not enough memory for their immediate execution. Hence, FMO may be able to complete the calculations whereas without such adaptations it aborts.
Computational method for general multicenter electronic structure calculations.
Batcho, P F
2000-06-01
Here a three-dimensional fully numerical (i.e., chemical basis-set free) method [P. F. Batcho, Phys. Rev. A 57, 6 (1998)], is formulated and applied to the calculation of the electronic structure of general multicenter Hamiltonian systems. The numerical method is presented and applied to the solution of Schrödinger-type operators, where a given number of nuclei point singularities is present in the potential field. The numerical method combines the rapid "exponential" convergence rates of modern spectral methods with the multiresolution flexibility of finite element methods, and can be viewed as an extension of the spectral element method. The approximation of cusps in the wave function and the formulation of multicenter nuclei singularities are efficiently dealt with by the combination of a coordinate transformation and a piecewise variational spectral approximation. The complete system can be efficiently inverted by established iterative methods for elliptical partial differential equations; an application of the method is presented for atomic, diatomic, and triatomic systems, and comparisons are made to the literature when possible. In particular, local density approximations are studied within the context of Kohn-Sham density functional theory, and are presented for selected subsets of atomic and diatomic molecules as well as the ozone molecule.
Quasiparticle GW calculations within the GPAW electronic structure code
DEFF Research Database (Denmark)
Hüser, Falco
properties are to a large extent governed by the physics on the atomic scale, that means pure quantum mechanics. For many decades, Density Functional Theory has been the computational method of choice, since it provides a fairly easy and yet accurate way of determining electronic structures and related......The GPAW electronic structure code, developed at the physics department at the Technical University of Denmark, is used today by researchers all over the world to model the structural, electronic, optical and chemical properties of materials. They address fundamental questions in material science...... with respect to the system one wants to investigate by choosing a certain functional or by tuning parameters. A succesful alternative is the so-called GW approximation. It is mathematically precise and gives a physically well-founded description of the complicated electron interactions in terms of screening...
Electronic-structure calculations of large cadmium chalcogenide nanoparticles
Energy Technology Data Exchange (ETDEWEB)
Frenzel, Johannes [Lehrstuhl fuer Theoretische Chemie, Ruhr-Universitaet Bochum (Germany); Joswig, Jan-Ole [Physikalische Chemie, Technische Universitaet Dresden (Germany)
2012-02-15
In this paper, we will review our studies of large cadmium chalcogenide nanoparticles and present some new results on cadmium telluride systems. All calculations have been performed using density-functional based methods. The studies deal with the structural properties of saturated and unsaturated nanoparticles where the surfactants generally are hydrogen atoms or thiol groups. We have focused on the investigation of the density of states, the Mulliken charges, the eigenvalue spectra, and the spatial distributions of the frontier orbitals. Optical excitation spectra of pure CdS and CdSe/CdS core-shell systems have been calculated using a linear-response formalism. The reviewed studies are compared to the state of the art of modeling large cadmium chalcogenide particles. Optical excitations in large saturated cadmium chalcogenide nanoparticles with several thousand atoms. (Copyright copyright 2012 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)
Accelerating VASP electronic structure calculations using graphic processing units
Hacene, Mohamed
2012-08-20
We present a way to improve the performance of the electronic structure Vienna Ab initio Simulation Package (VASP) program. We show that high-performance computers equipped with graphics processing units (GPUs) as accelerators may reduce drastically the computation time when offloading these sections to the graphic chips. The procedure consists of (i) profiling the performance of the code to isolate the time-consuming parts, (ii) rewriting these so that the algorithms become better-suited for the chosen graphic accelerator, and (iii) optimizing memory traffic between the host computer and the GPU accelerator. We chose to accelerate VASP with NVIDIA GPU using CUDA. We compare the GPU and original versions of VASP by evaluating the Davidson and RMM-DIIS algorithms on chemical systems of up to 1100 atoms. In these tests, the total time is reduced by a factor between 3 and 8 when running on n (CPU core + GPU) compared to n CPU cores only, without any accuracy loss. © 2012 Wiley Periodicals, Inc.
Spectral-Product Methods for Electronic Structure Calculations (Postprint)
2007-06-12
and electronically excited potential energy surfaces in Monte Carlo and molecular dynamics simula- tions of singly doped inert-gas clusters [27], the...Matsunaga N, Nguyen KA, Su SJ, Windus TL, Dupuis M, Montgomery JA (1993) J Comput Chem 14:1347 3. Pauli W (1925) Z Physik 31:765 4. Heisenberg W (1926) Z...Physik 38:411 5. Heisenberg W (1926) Z Physik 39:499 6. Heisenberg W (1926) Z Physik 40:501 7. Dirac PAM (1926) Proc R Soc (London) A 112:661 8
First principles calculations of the structural and electronic properties of(CdSe)n clusters
Institute of Scientific and Technical Information of China (English)
WANG Xin-qiang; CHEN Yong
2004-01-01
The structural and electronic properties of (CdSe)n(1≤n≤5) clusters are calculated using density functional theory within the pseudopotential and generalized gradient approximations. The calculated binding energies and highest occupied molecular orbitallowest unoccupied molecular orbital gaps are compared with those obtained within local density approximation.
Calculation of the valence electron structures of alloying cementite and its biphase interface
Institute of Scientific and Technical Information of China (English)
刘志林; 李志林; 刘伟东
2001-01-01
The valence electron structures of alloying cementite θ-(Fe, M)3C and ε-(Fe, M)3C andthose of the biphase interfaces between them and α-Fe are calculated with Yu's empirical electrontheory of solid and molecules. The calculation results accord with the actual behavior of alloys.
Regularizing the molecular potential in electronic structure calculations. II. Many-body methods
Energy Technology Data Exchange (ETDEWEB)
Bischoff, Florian A., E-mail: florian.bischoff@hu-berlin.de [Institut für Chemie, Humboldt-Universität zu Berlin, Unter den Linden 6, 10099 Berlin (Germany)
2014-11-14
In Paper I of this series [F. A. Bischoff, “Regularizing the molecular potential in electronic structure calculations. I. SCF methods,” J. Chem. Phys. 141, 184105 (2014)] a regularized molecular Hamilton operator for electronic structure calculations was derived and its properties in SCF calculations were studied. The regularization was achieved using a correlation factor that models the electron-nuclear cusp. In the present study we extend the regularization to correlated methods, in particular the exact solution of the two-electron problem, as well as second-order many body perturbation theory. The nuclear and electronic correlation factors lead to computations with a smaller memory footprint because the singularities are removed from the working equations, which allows coarser grid resolution while maintaining the precision. Numerical examples are given.
Non-primitive rectangular cells for tight-binding electronic structure calculations
Boykin, Timothy; Kharche, Neerav; Klimeck, Gerhard
2009-01-01
Rectangular non-primitive unit cells are computationally convenient for use in nanodevice electronic structure and transport calculations. When these cells are used for Calculations of structures with periodicity, the resulting bands are zone-folded and must be unfolded in order to identify important gaps and masses. Before the zone-unfolding method can be applied, one must first determine the allowed wavevectors for the specific non-primitive cell. Because most computationally convenient non...
Non-Primitive Rectangular Cells for Tight-Binding Electronic Structure Calculations
Boykin, Timothy B.
2008-01-01
Rectangular non-primitive unit cells are computationally convenient for use in nanodevice electronic structure and transport calculations. When these cells are used for calculations of structures with periodicity, the resulting bands are zone-folded and must be unfolded in order to identify important gaps and masses. Before the zone-unfolding method can be applied, one must first determine the allowed wavevectors for the specific non-primitive cell. Because most computationally convenient ...
Ab-initio calculations of electronic structure and optical properties of TiAl alloy
Hussain, Altaf; Sikandar Hayat, Sardar; Choudhry, M. A.
2011-05-01
The electronic structures and optical properties of TiAl intermetallic alloy system are studied by the first-principle orthogonalized linear combination of atomic orbitals method. Results on the band structure, total and partial density of states, localization index, effective atomic charges, and optical conductivity are presented and discussed in detail. Total density of states spectra reveal that (near the Fermi level) the majority of the contribution is from Ti-3d states. The effective charge calculations show an average charge transfer of 0.52 electrons from Ti to Al in primitive cell calculations of TiAl alloy. On the other hand, calculations using supercell approach reveal an average charge transfer of 0.48 electrons from Ti to Al. The localization index calculations, of primitive cell as well as of supercell, show the presence of relatively localized states even above the Fermi level for this alloy. The calculated optical conductivity spectra of TiAl alloy are rich in structures, showing the highest peak at 5.73 eV for supercell calculations. Calculations of the imaginary part of the linear dielectric function show a prominent peak at 5.71 eV and a plateau in the range 1.1-3.5 eV.
AMORPHOUS SILICON ELECTRONIC STRUCTURE MODELING AND BASIC ELECTRO-PHYSICAL PARAMETERS CALCULATION
Directory of Open Access Journals (Sweden)
B. A. Golodenko
2014-01-01
Full Text Available Summary. The amorphous semiconductor has any unique processing characteristics and it is perspective material for electronic engineering. However, we have not authentic information about they atomic structure and it is essential knot for execution calculation they electronic states and electro physical properties. The author's methods give to us decision such problem. This method allowed to calculation the amorphous silicon modeling cluster atomics Cartesian coordinates, determined spectrum and density its electronic states and calculation the basics electro physical properties of the modeling cluster. At that determined numerical means of the energy gap, energy Fermi, electron concentration inside valence and conduction band for modeling cluster. The find results provides real ability for purposeful control to type and amorphous semiconductor charge carriers concentration and else provides relation between atomic construction and other amorphous substance physical properties, for example, heat capacity, magnetic susceptibility and other thermodynamic sizes.
Ab initio calculations of electronic structure of anatase TiO2
Institute of Scientific and Technical Information of China (English)
Chen Qiang; Cao Hong-Hong
2004-01-01
This paper presents the results of the self-consistent calculations on the electronic structure of anatase phase of TiO2. The calculations were performed using the full potential-linearized augmented plane wave method (FP-LAPW)in the framework of the density functional theory (DFT) with the generalized gradient approximation (GGA). The fully optimized structure, obtained by minimizing the total energy and atomic forces, is in good agreement with experiment.We also calculated the band structure and the density of states. In particular, the calculated band structure prefers an indirect transition between wlence and conduction bands of anatase TiO2, which may be helpful for clarifying the ambiguity in other theoretical works.
Dynamical mean field theory-based electronic structure calculations for correlated materials.
Biermann, Silke
2014-01-01
We give an introduction to dynamical mean field approaches to correlated materials. Starting from the concept of electronic correlation, we explain why a theoretical description of correlations in spectroscopic properties needs to go beyond the single-particle picture of band theory.We discuss the main ideas of dynamical mean field theory and its use within realistic electronic structure calculations, illustrated by examples of transition metals, transition metal oxides, and rare-earth compounds. Finally, we summarise recent progress on the calculation of effective Hubbard interactions and the description of dynamical screening effects in solids.
Energy Technology Data Exchange (ETDEWEB)
Aguiar, J; Asta, M; Gronbech-Jensen, N; Perlov, A; Milman, V; Gao, S; Pickard, C; Browning, N
2009-06-05
Energy loss spectra from a variety of cubic oxides are compared with ab-initio calculations based on the density functional plane wave method (CASTEP). In order to obtain agreement between experimental and theoretical spectra, unique material specific considerations were taken into account. The spectra were calculated using various approximations to describe core-hole effects and electronic correlations. All the calculations are based on the local spin density approximation to show qualitative agreement with the sensitive oxygen K-edge spectra in ceria, zirconia, and urania. Comparison of experimental and theoretical results let us characterize the main electronic interactions responsible for both the electronic structure and the resulting EEL spectra of the compounds in question.
Bannikov, V. V.; Shein, I. R.; Ivanovskii, A. L.
2010-05-01
First-principles FLAPW-GGA calculations for six possible polymorphs of ruthenium mononitride RuN indicate that the most stable structure is that of zinc blende rather than the rock salt structure recently reported for synthesized RuN samples. The elastic, electronic properties and the features of chemical bonds of zinc-blende RuN polymorph were investigated and discussed in detail.
Electronic Structure Calculations for Heavy Elements: Radon (Z=86) and Francium (Z=87)
Koufos, Alexander; Papaconstantopoulos, Dimitrios
2010-03-01
Electronic structure calculations allow scientists to predict the properties of solids without the use of physical material. Although the ability to manipulate matter has improved dramatically within the past couple decades, some matter is still hard to study. Modern computers not only let us study this matter, but allow us to do it more quickly and just as accurately. The electronic structure of two rare and mostly unstudied elements, Radon (Z=86) and Francium (Z=87), has been calculated. The augmented plane wave (APW) method with local density approximation (LDA) functional as well as the linearized augmented plane wave (LAPW) method with both LDA and generalized gradient approximation (GGA) functionals were used to perform the calculations. Francium total energy calculations gave the fcc structure slightly below the bcc structure with a minimal energy difference of δE=0.33mRy. The difference found is consistent with other alkali metal total energy calculations which do not verify the bcc structure to be the ground state. Radon was predicted to be an insulator with a gap of 0.931 Ry similar to the other noble gases.
Institute of Scientific and Technical Information of China (English)
无
2010-01-01
The valence electron structure (VES) of RuB2 and OsB2 were calculated by the empirical electron theory (EET) of solids and molecules and compared with the results derived from the first-principles calculations. The distributions of covalent electrons in different bonds indicate that B-B and B-Me have remarkably covalent bonding characters. Lattice electrons cruising around Me-Me layers are found to have great influences on electronic conductivity and high temperature plasticity. The ultra-high values of elastic constant Cn in the two compounds originate from close-packed covalent bonding along the c axis. Uneven bond strengths and distributions of covalent bonds, especially for B-Afe bonds, yield significant anisotropy. Low ratios of lattice electrons to covalent electrons suggest the intrinsic embrittlement in crystals. The fact that the calculated cohesive energies well agree with experimental results demonstrates the good suitability of the EET calculations in estimating cohesive energy for transition-metal borides.
Landau, Arie; Kaprálová-Žďánská, Petra Ruth; Moiseyev, Nimrod
2015-01-01
Complex eigenvalues, resonances, play an important role in large variety of fields in physics and chemistry. For example, in cold molecular collision experiments and electron scattering experiments, autoionizing and pre-dissociative metastable resonances are generated. However, the computation of complex resonance eigenvalues is difficult, since it requires severe modifications of standard electronic structure codes and methods. Here we show how resonance eigenvalues, positions and widths, can be calculated using the standard, widely used, electronic-structure packages. Our method enables the calculations of the complex resonance eigenvalues by using analytical continuation procedures (such as Pad\\'{e}). The key point in our approach is the existence of narrow analytical passages from the real axis to the complex energy plane. In fact, the existence of these analytical passages relies on using finite basis sets. These passages become narrower as the basis set becomes more complete, whereas in the exact limit,...
Takaba, Hiromitsu; Kimura, Shou; Alam, Md. Khorshed
2017-03-01
Durability of organo-lead halide perovskite are important issue for its practical application in a solar cells. In this study, using density functional theory (DFT) and molecular dynamics, we theoretically investigated a crystal structure, electronic structure, and ionic diffusivity of the partially substituted cubic MA0.5X0.5PbI3 (MA = CH3NH3+, X = NH4+ or (NH2)2CH+ or Cs+). Our calculation results indicate that a partial substitution of MA induces a lattice distortion, resulting in preventing MA or X from the diffusion between A sites in the perovskite. DFT calculations show that electronic structures of the investigated partially substituted perovskites were similar with that of MAPbI3, while their bandgaps slightly decrease compared to that of MAPbI3. Our results mean that partial substitution in halide perovskite is effective technique to suppress diffusion of intrinsic ions and tune the band gap.
Electronic Structure of KFe2Se2 from First-Principles Calculations
Institute of Scientific and Technical Information of China (English)
CAO Chao; DAI Jian-Hui
2011-01-01
@@ Electronic structures and magnetic properties for iron-selenide KFe2Se2 axe studied by first-principles calculations.The ground state is collinear antiferromagnetic with calculated 2.26μB magnetic moment on Fe atoms; and the J1 and J2 coupling strengths are calculated to be 0.038eV and 0.029eV.The states around EF are dominated by the Fe 3d orbitals which hybridize noticeably to the Se 4p orbitals.While the band structure of KFe2Se2 is similar to a heavily electron-doped BaFe2As2 or FeSe system,the Fermi surface of KFe2Se2 is much closer to the FeSe system since the electron sheets around M are symmetric with respect to x-y exchange.These features,as well as the absence of Fermi surface nesting,suggest that the parent KFe2Se2 could be regarded as an electron doped FeSe system with possible local moment magnetism.%Electronic structures and magnetic properties for iron-selenide KFe2Se2 are studied by first-principles calculations.The ground state is collinear antiferromagnetic with calculated 2.26μB magnetic moment on Fe atoms; and the J1 and J2 coupling strengths are calculated to be 0.038eV and 0.029eV.The states around EF are dominated by the Fe 3d orbitals which hybridize noticeably to the Se 4p orbitals.While the band structure of KFe2Se2 is similar to a heavily electron-doped BaFe2As2 or FeSe system, the Fermi surface of KFe2Se2 is much closer to the FeSe system since the electron sheets around M are symmetric with respect to x-y exchange.These features, as well as the absence of Fermi surface nesting, suggest that the parent KFe2Se2 could be regarded as an electron doped FeSe system with possible local moment magnetism.
Minimal parameter implicit solvent model for ab initio electronic structure calculations
Dziedzic, Jacek; Skylaris, Chris-Kriton; Mostofi, Arash A; Payne, Mike C
2011-01-01
We present an implicit solvent model for ab initio electronic structure calculations which is fully self-consistent and is based on direct solution of the nonhomogeneous Poisson equation. The solute cavity is naturally defined in terms of an isosurface of the electronic density according to the formula of Fattebert and Gygi (J. Comp. Chem. 23, 6 (2002)). While this model depends on only two parameters, we demonstrate that by using appropriate boundary conditions and dispersion-repulsion contributions, solvation energies obtained for an extensive test set including neutral and charged molecules show dramatic improvement compared to existing models. Our approach is implemented in, but not restricted to, a linear-scaling density functional theory (DFT) framework, opening the path for self-consistent implicit solvent DFT calculations on systems of unprecedented size, which we demonstrate with calculations on a 2615-atom protein-ligand complex.
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Electronic structure calculations of rare-earth intermetallic compound YAg using ab initio methods
Institute of Scientific and Technical Information of China (English)
(S).U(g)ur; G.U(g)ur; F.Soyalp; R.Ellialtio(g)lu
2009-01-01
The structural,elastic and electronic properties of YAg-B2(CsC1) were investigated using the first-principles calculations.The energy band structure and the density of states were studied in detail,including partial density of states (PDOS),in order to identify the character of each band.The structural parameters (lattice constant,bulk modulus,pressure derivative of bulk modulus) and elastic constants were also obtained.The results were consistent with the experimental data available in the literature,as well as other theoretical results.
Density functional calculation of equilibrium geometry and electronic structure of pyrite
Institute of Scientific and Technical Information of China (English)
邱冠周; 肖奇; 胡岳华; 徐竞
2001-01-01
The equilibrium geometry and electronic structure of pyrite has been studied using self-consistent density-functional theory within the local density approximation (LDA). The optimum bulk geometry is in good agreement with crystallographic data. The calculated band structure and density of states in the region around the Fermi energy show that valence-band maximum (VBM) is at X (100), and the conduction-band minimum (CBM) is at G (000). The indirect and direct band gaps are 0.6eV and 0.74eV, respectively. The calculated contour map of difference of charge density shows excess charge in nonbonding d electron states on the Fe sites. The density increases between sulfur nuclei and between iron and sulfur nuclei qualitatively reveal that S-S bond and Fe-S bond are covalent binding.
A proposal to first principles electronic structure calculation: Symbolic-Numeric method
Kikuchi, Akihito
2012-01-01
This study proposes an approach toward the first principles electronic structure calculation with the aid of symbolic-numeric solving. The symbolic computation enables us to express the Hartree-Fock-Roothaan equation in an analytic form and approximate it as a set of polynomial equations. By use of the Grobner basis technique, the polynomial equations are transformed into other ones which have identical roots. The converted equations take more convenient forms which will simplify numerical procedures, from which we can derive necessary physical properties in order, in an a la carte way. This method enables us to solve the electronic structure calculation, the optimization of any kind, or the inverse problem as a forward problem in a unified way, in which there is no need for iterative self-consistent procedures with trials and errors.
Xu, C.; Li, Q.; Liu, C. M.; Duan, M. Y.; Wang, H. K.
2016-05-01
First-principles calculations are employed to investigate the structural and elastic properties, formation enthalpies and chemical bonding features as well as hardness values of chromium tetraboride (CrB4) with different structures. The lattice parameters, Poisson’s ratio and B/G ratio are also derived. Our calculations indicate that the orthorhombic structure with Pnnm symmetry is the most energetically stable one for CrB4. Except for WB4P63/mmc structure with imaginary frequencies, another six new structures are investigated through the full phonon dispersion calculations. Their mechanical and thermodynamic stabilities are also studied by calculating the elastic constants and formation enthalpies. Our calculations show that the thermodynamic stabilities of all these CrB4 phases can be enhanced under high pressure. The large shear moduli, Young’s moduli and hardness values indicate that these CrB4 phases are potential hard materials. Analyses of the densities of states (DOSs) and electron localization functions (ELFs) provide further understandings of the chemical and physical properties of these CrB4 phases. It is observed that the large occupations and high strengths of the B-B covalent bonds are important for the stabilities, incompressibility and hardnesses of these CrB4 phases.
Lin, Lin
2012-01-01
We describe how to apply the recently developed pole expansion plus selected inversion (PEpSI) technique to Kohn-Sham density function theory (DFT) electronic structure calculations that are based on atomic orbital discretization. We give analytic expressions for evaluating charge density, total energy, Helmholtz free energy and atomic forces without using the eigenvalues and eigenvectors of the Kohn-Sham Hamiltonian. We also show how to update the chemical potential without using Kohn-Sham...
ding,Yi; Wang, Yanli
2015-01-01
Using first-principles calculations, we investigate the geometric structures and electronic properties of porous silicene and germanene nanosheets, which are the Si and Ge analogues of α−graphyne (referred to as silicyne and germanyne). It is found that the elemental silicyne and germanyne sheets are energetically unfavourable. However, after the C-substitution, the hybrid graphyne-like sheets (c-silicyne/c-germanyne) possess robust energetic and dynamical stabilities. Different from silicene...
Multi-Center Electronic Structure Calculations for Plasma Equation of State
Energy Technology Data Exchange (ETDEWEB)
Wilson, B G; Johnson, D D; Alam, A
2010-12-14
We report on an approach for computing electronic structure utilizing solid-state multi-center scattering techniques, but generalized to finite temperatures to model plasmas. This approach has the advantage of handling mixtures at a fundamental level without the imposition of ad hoc continuum lowering models, and incorporates bonding and charge exchange, as well as multi-center effects in the calculation of the continuum density of states.
Efficient electronic structure calculation for molecular ionization dynamics at high x-ray intensity
Directory of Open Access Journals (Sweden)
Yajiang Hao
2015-07-01
Full Text Available We present the implementation of an electronic-structure approach dedicated to ionization dynamics of molecules interacting with x-ray free-electron laser (XFEL pulses. In our scheme, molecular orbitals for molecular core-hole states are represented by linear combination of numerical atomic orbitals that are solutions of corresponding atomic core-hole states. We demonstrate that our scheme efficiently calculates all possible multiple-hole configurations of molecules formed during XFEL pulses. The present method is suitable to investigate x-ray multiphoton multiple ionization dynamics and accompanying nuclear dynamics, providing essential information on the chemical dynamics relevant for high-intensity x-ray imaging.
Efficient electronic structure calculation for molecular ionization dynamics at high x-ray intensity
Hao, Yajiang; Hanasaki, Kota; Son, Sang-Kil; Santra, Robin
2015-01-01
We present the implementation of an electronic-structure approach dedicated to ionization dynamics of molecules interacting with x-ray free-electron laser (XFEL) pulses. In our scheme, molecular orbitals for molecular core-hole states are represented by linear combination of numerical atomic orbitals that are solutions of corresponding atomic core-hole states. We demonstrate that our scheme efficiently calculates all possible multiple-hole configurations of molecules formed during XFEL pulses. The present method is suitable to investigate x-ray multiphoton multiple ionization dynamics and accompanying nuclear dynamics, providing essential information on the chemical dynamics relevant for high-intensity x-ray imaging.
The LDA+U calculation of electronic band structure of GaAs
Bahuguna, B. P.; Sharma, R. O.; Saini, L. K.
2016-05-01
We present the electronic band structure of bulk gallium arsenide (GaAs) using first principle approach. A series of calculations has been performed by applying norm-conserving pseudopotentials and ultrasoft non-norm-conserving pseudopotentials within the density functional theory. These calculations yield too small band gap as compare to experiment. Thus, we use semiemperical approach called local density approximation plus the multi-orbital mean-field Hubbard model (LDA+U), which is quite effective in order to describe the band gap of GaAs.
Ab initio calculations of the electronic structure and bonding characteristics of LaB6
Hossain, Faruque M.; Riley, Daniel P.; Murch, Graeme E.
2005-12-01
Lanthanum hexaboride ( LaB6 , NIST SRM-660a) is widely used as a standard reference material for calibrating the line position and line shape parameters of powder diffraction instruments. The accuracy of this calibration technique is highly dependent on how completely the reference material is characterized. Critical to x-ray diffraction, this understanding must include the valence of the La atomic position, which in turn will influence the x-ray form factor (f) and hence the diffracted intensities. The electronic structure and bonding properties of LaB6 have been investigated using ab initio plane-wave pseudopotential total energy calculations. The electronic properties and atomic bonding characteristics were analyzed by estimating the energy band structure and the density of states around the Fermi energy level. The calculated energy band structure is consistent with previously reported experimental findings; de Haas-van Alphen and two-dimensional angular correlation of electron-positron annihilation radiation. In addition, the bond strengths and types of atomic bonds in the LaB6 compound were estimated by analyzing the Mulliken charge density population. The calculated result revealed the coexistence of covalent, ionic, and metallic bonding in the LaB6 system and partially explains its high efficiency as a thermionic emitter.
A novel Gaussian-Sinc mixed basis set for electronic structure calculations
Jerke, Jonathan L.; Lee, Young; Tymczak, C. J.
2015-08-01
A Gaussian-Sinc basis set methodology is presented for the calculation of the electronic structure of atoms and molecules at the Hartree-Fock level of theory. This methodology has several advantages over previous methods. The all-electron electronic structure in a Gaussian-Sinc mixed basis spans both the "localized" and "delocalized" regions. A basis set for each region is combined to make a new basis methodology—a lattice of orthonormal sinc functions is used to represent the "delocalized" regions and the atom-centered Gaussian functions are used to represent the "localized" regions to any desired accuracy. For this mixed basis, all the Coulomb integrals are definable and can be computed in a dimensional separated methodology. Additionally, the Sinc basis is translationally invariant, which allows for the Coulomb singularity to be placed anywhere including on lattice sites. Finally, boundary conditions are always satisfied with this basis. To demonstrate the utility of this method, we calculated the ground state Hartree-Fock energies for atoms up to neon, the diatomic systems H2, O2, and N2, and the multi-atom system benzene. Together, it is shown that the Gaussian-Sinc mixed basis set is a flexible and accurate method for solving the electronic structure of atomic and molecular species.
Energy Technology Data Exchange (ETDEWEB)
Liu, X.X.; Liu, L.Z. [Key Laboratory of Modern Acoustics, MOE, Institute of Acoustics and Collaborative Innovation Center of Advanced Microstructures, National Laboratory of Solid State Microstructures, Nanjing University, Nanjing 210093 (China); Wu, X.L., E-mail: hkxlwu@nju.edu.cn [Key Laboratory of Modern Acoustics, MOE, Institute of Acoustics and Collaborative Innovation Center of Advanced Microstructures, National Laboratory of Solid State Microstructures, Nanjing University, Nanjing 210093 (China); Department of Physics, NingBo University, NingBo 315301 (China); Chu, Paul K. [Department of Physics and Materials Science, City University of Hong Kong, Tat Chee Avenue, Kowloon, Hong Kong (China)
2015-07-03
The defect states and optical absorption enhancement induced by twin boundaries in silicon are investigated by first-principle calculation. The defect states in the forbidden bands are identified and based on the established electronic structures, the dielectric functions and absorption coefficients are derived. An important result of our calculations is that visible light absorption by the twinning configuration is enhanced significantly, indicating that twinning structures possibly play an important role in silicon-based photovoltaic devices. - Highlights: • Defect states and optical absorption enhancement induced by twin boundaries in silicon are investigated theoretically. • Dielectric functions and absorption coefficients are derived. • Enhanced visible light absorption by the twinning configuration is demonstrated. • Twinning structures play an important role in silicon-based photovoltaic devices.
Directory of Open Access Journals (Sweden)
Yu Wang
2002-01-01
Full Text Available Abstract:We investigate a theoretical model of molecular metalwire constructed from linear polynuclear metal complexes. In particular we study the linear Crn metal complex and Cr molecular metalwire. The electron density distributions of the model nanowire and the linear Crn metal complexes, with n = 3, 5, and 7, are calculated by employing CRYSTAL98 package with topological analysis. The preliminary results indicate that the bonding types between any two neighboring Cr are all the same, namely the polarized open-shell interaction. The pattern of electron density distribution in metal complexes resembles that of the model Cr nanowire as the number of metal ions increases. The conductivity of the model Cr nanowire is also tested by performing the band structure calculation.
Ab initio calculations on twisted graphene/hBN: Electronic structure and STM image simulation
Correa, J. D.; Cisternas, E.
2016-09-01
By performing ab initio calculations we obtained theoretical scanning tunneling microscopy (STM) images and studied the electronic properties of graphene on a hexagonal boron-nitrite (hBN) layer. Three different stack configurations and four twisted angles were considered. All calculations were performed using density functional theory, including van der Waals interactions as implemented in the SIESTA ab initio package. Our results show that the electronic structure of graphene is preserved, although some small changes are induced by the interaction with the hBN layer, particularly in the total density of states at 1.5 eV under the Fermi level. When layers present a twisted angle, the density of states shows several van Hove singularities under the Fermi level, which are associated to moiré patterns observed in theoretical STM images.
Energy Technology Data Exchange (ETDEWEB)
Mehrabova, M. A., E-mail: Mehrabova@mail.ru; Madatov, R. S. [Azerbaijan National Academy of Sciences, Institute of Radiation Problems (Azerbaijan)
2011-08-15
The Green's functions theory and the bond-orbital model are used as a basis for calculations of the electron structure of local defects-specifically, vacancies and their compensated states in III-VI semiconductors. The energy levels in the band gap are established, and the changes induced in the electron densities in the GaS, GaSe, and InSe semiconductors by anion and cation vacancies and their compensated states are calculated. It is established that, if a vacancy is compensated by an atom of an element from the same subgroup with the same tetrahedral coordination and if the ionic radius of the compensating atom is smaller than that of the substituted atom, the local levels formed by the vacancy completely disappear. It is shown that this mechanism of compensation of vacancies provides a means not only for recovering the parameters of the crystal, but for improving the characteristics of the crystal as well.
Roondhe, Basant; Upadhyay, Deepak; Som, Narayan; Pillai, Sharad B.; Shinde, Satyam; Jha, Prafulla K.
2017-03-01
The structural, electronic, dynamical and thermodynamical properties of CmX (X = N, P, As, Sb, and Bi) compounds are studied using first principles calculations within density functional theory. The Perdew-Burke-Ernzerhof spin polarized generalized gradient approximation and Perdew-Wang (PW) spin polarized local density approximation as the exchange correlational functionals are used in these calculations. There is a good agreement between the present and previously reported data. The calculated electronic density of states suggests that the curium monopnictides are metallic in nature, which is consistent with earlier studies. The significant values of magnetic moment suggest their magnetic nature. The phonon dispersion curves and phonon density of states are also calculated, which depict the dynamical stability of these compounds. There is a significant separation between the optical and acoustical phonon branches. The temperature dependence of the thermodynamical functions are also calculated and discussed. Internal energy and vibrational contribution to the Helmholtz free energy increases and decreases, respectively, with temperature. The entropy increases with temperature. The specific heat at constant volume and Debye temperature obey Debye theory. The temperature variation of the considered thermodynamical functions is in line with those of other crystalline solids.
First-principles calculations of BC{sub 4}N nanostructures: stability and electronic structure
Energy Technology Data Exchange (ETDEWEB)
Freitas, A.; Azevedo, S. [Universidade Federal da Paraiba, CCEN, Departamento de Fisica, Joao Pessoa, PB (Brazil); Machado, M. [Universidade Federal de Pelotas, Departamento de Fisica, Pelotas, RS (Brazil); Kaschny, J.R. [Instituto Federal da Bahia-Campus Vitoria da Conquista, Vitoria da Conquista, BA (Brazil)
2012-07-15
In this work, we apply first-principles methods to investigate the stability and electronic structure of BC{sub 4}N nanostructures which were constructed from hexagonal graphite layers where substitutional nitrogen and boron atoms are placed at specific sites. These layers were rolled up to form zigzag and armchair nanotubes, with diameters varying from 7 to 12 A, or cut and bent to form nanocones, with 60 and 120 disclination angles. The calculation results indicate that the most stable structures are the ones which maximize the number of B-N and C-C bonds. It is found that the zigzag nanotubes are more stable than the armchair ones, where the strain energy decreases with increasing tube diameter D, following a 1/D {sup 2} law. The results show that the 60 disclination nanocones are the most stable ones. Additionally, the calculated electronic properties indicate a semiconducting behavior for all calculated structures, which is intermediate to the typical behaviors found for hexagonal boron nitride and graphene. (orig.)
ACRES: An Efficient Method for First-Principles Electronic Structure Calculations of Complex Systems
Energy Technology Data Exchange (ETDEWEB)
WAGHMARE,R.V.; KIM,HANCHUL; PARK,I.J.; MODINE,NORMAND A.; MARAGAKIS,P.; KAXIRAS,EFTHIMIOS
2000-08-29
The authors discuss their new implementation of the Adaptive Coordinate Real-space Electronic Structure (ACRES) method for studying the atomic and electronic structure of infinite periodic as well as finite systems, based on density functional theory. This improved version aims at making the method widely applicable and efficient, using high performance Fortran on parallel architectures. The scaling of various parts of an ACRES calculation is analyzed and compared to that of plane-wave based methods. The new developments that lead to enhanced performance, and their parallel implementation, are presented in detail. They illustrate the application of ACRES to the study of elemental crystalline solids, molecules and complex crystalline materials, such as blue bronze and zeolites.
Structural and electronic phase transitions of ThS2 from first-principles calculations
Guo, Yongliang; Wang, Changying; Qiu, Wujie; Ke, Xuezhi; Huai, Ping; Cheng, Cheng; Zhu, Zhiyuan; Chen, Changfeng
2016-10-01
Thorium and its compounds have received considerable attention in recent years due to the renewed interest in developing the thorium fuel cycle as an alternative nuclear energy technology. There is pressing current need to explore the physical properties essential to the fundamental understanding and practical application of these materials. Here we report on a computational study of thorium disulfide (ThS2), which plays an important role in the thorium fuel reprocessing cycle. We have employed the density functional theory and evolutionary structure search methods to determine the crystal structures, electronic band structures, phonon dispersions and density of states, and thermodynamic properties of ThS2 under various pressure and temperature conditions. Our calculations identify several crystalline phases of ThS2 and a series of structural phase transitions induced by pressure and temperature. The calculated results also reveal electronic phase transitions from the semiconducting state in the low-pressure phases of ThS2 in the P n m a and F m 3 ¯m symmetry to the metallic state in the high-pressure phases of ThS2 in the P n m a and I 4 /m m m symmetry. These results explain the experimental observation of the thermodynamic stability of the P n m a phase of ThS2 at the ambient conditions and a pressure-induced structural phase transition in ThS2 around 40 GPa. Moreover, the present study reveals considerable additional information on the structural and electronic properties of ThS2 in a wide range of pressure and temperature. Such information provides key insights into the fundamental material behavior and the underlying mechanisms that lay the foundation for further exploration and application of ThS2.
Electronic Structure of Cu(tmdt2 Studied with First-Principles Calculations
Directory of Open Access Journals (Sweden)
Kiyoyuki Terakura
2012-08-01
Full Text Available We have studied the electronic structure of Cu(tmdt2, a material related to single-component molecular conductors, by first-principles calculations. The total energy calculations for several different magnetic configurations show that there is strong antiferromagnetic (AFM exchange coupling along the crystal a-axis. The electronic structures are analyzed in terms of the molecular orbitals near the Fermi level of isolated Cu(tmdt2 molecule. This analysis reveals that the system is characterized by the half-filled pdσ(− band whose intermolecular hopping integrals have strong one-dimensionality along the crystal a-axis. As the exchange splitting of the band is larger than the band width, the basic mechanism of the AFM exchange coupling is the superexchange. It will also be shown that two more ligand orbitals which are fairly insensitive to magnetism are located near the Fermi level. Because of the presence of these orbitals, the present calculation predicts that Cu(tmdt2 is metallic even in its AFM state, being inconsistent with the available experiment. Some comments will be made on the difference between Cu(tmdt2 and Cu(dmdt2.
Structural and electronic properties of cerium from LDA+U calculations
Directory of Open Access Journals (Sweden)
F. Kheradmand
2008-12-01
Full Text Available In this work structural, electronic and magnetic properties of alpha and gamma phases of cerium crystal have been calculated by means of the LDA and LDA+U methods. The equilibrium volume and magnetic moment obtained from the GGA approximation in agreement with the experiment are equal to 27.64 Å3 and 0.00018 µB, respectively. This agreement shows that the 4f electrons in alpha phase are itinerant due to the use of the GGA, where no strong correlations have been yet thaken into account. We have observed that even after applying the GGA+U method with U = 6.1 eV, the density of states of f orbital remains still at Fermi surface. Therefore, in complete accord with the experiment, our results show that the 4f electrons in the alpha phase are not localized. This is the case where the LDA and the GGA approximations could not describe the gamma phase properly. Indeed, physical properties of the gamma phase is consistent with the experiment and could only be reproduced after applying LDA+U method with U = 4.4 eV. In this way, the value of equilibrium volume and magnetic moment calculated for the gamma phase were found to be 34.33 Å3 and 1.15 µB, respectively. After including correlations among 4f electrons the γ-Ce DOS is positioned at its more reasonable place lower than Fermi level compared with the DOS obtained from GGA calculations. Our results, then, show that the 4f electrons in the gamma phase, as opposed to the alpha phase, are localized which is indicative of the fact that gamma cerium is a strongly correlated system. The volume of 11 kbar has been obtained for the pressure of the alpha-gamma phase transition .
A Linear Scaling Three Dimensional Fragment Method for Large ScaleElectronic Structure Calculations
Energy Technology Data Exchange (ETDEWEB)
Wang, Lin-Wang; Zhao, Zhengji; Meza, Juan
2007-07-26
We present a novel linear scaling ab initio total energyelectronic structure calculation method, which is simple to implement,easily to parallelize, and produces essentially thesame results as thedirect ab initio method, while it could be thousands of times faster.Using this method, we have studied the dipole moments of CdSe quantumdots, and found both significant bulk and surface contributions. The bulkdipole contribution cannot simply be estimated from the bulk spontaneouspolarization value by a proportional volume factor. Instead it has ageometry dependent screening effect. The dipole moment also produces astrong internal electric field which induces a strong electron holeseparation.
Energy Technology Data Exchange (ETDEWEB)
Umicevic, A.; Belosevic-Cavor, J.; Koteski, V.; Cekic, B.; Ivanovski, V. [Inst. of Nuclear Sciences Vinca, Lab. for Nuclear and Plasma Physics, Belgrade (Yugoslavia)
2009-09-15
A detailed theoretical study of the structure and electric field gradients (EFG) of the Zr{sub 2}Ni compound is presented. Using all-electron augmented plane waves plus local orbitals formalism, the equilibrium volume, bulk modulus, and EFGs at both non-equivalent crystallographic positions, Zr and Ni, are calculated. The possible mechanism of formation of the EFGs at both sites are analyzed and discussed. We have also performed supercell calculations with Cd and Ta impurities. Through the comparison of theoretical and experimental EFGs in these cases, we elucidate the role played by the Cd and Ta probe atoms in the time-differential perturbed angular correlation measurements of this compound. (orig.)
Calculated electronic and magnetic structure of screw dislocations in alpha iron
Energy Technology Data Exchange (ETDEWEB)
Odbadrakh, K.; Rusanu, A.; Stocks, G. Malcolm; Samolyuk, G. D.; Eisenbach, M.; Wang, Yang; Nicholson, D. M.
2011-01-01
Local atomic magnetic moments in crystalline Fe are perturbed by the presence of dislocations. The effects are most pronounced near the dislocation core and decay slowly as the strain field of the dislocation decreases with distance. We have calculated local moments using the locally self-consistent multiple scattering (LSMS) method for a supercell containing a screw-dislocation quadrupole. Finite size effects are found to be significant indicating that dislocation cores affect the electronic structure and magnetic moments of neighboring dislocations. The influence of neighboring dislocations points to a need to study individual dislocations from first principles just as they appear amid surrounding atoms in large-scale classical force field simulations. An approach for the use of the LSMS to calculate local moments in subvolumes of large atomic configurations generated in the course of classical molecular dynamics simulation of dislocationdynamics is discussed.
Calculated electronic and magnetic structure of screw dislocations in alpha iron
Energy Technology Data Exchange (ETDEWEB)
Odbadrakh, Khorgolkhuu [ORNL; Rusanu, Aurelian [ORNL; Stocks, George Malcolm [ORNL; Samolyuk, German D [ORNL; Eisenbach, Markus [ORNL; Wang, Yang Nmn [ORNL; Nicholson, Don M [ORNL
2011-01-01
Local atomic magnetic moments in crystalline Fe are perturbed by the presence of dislocations. The effects are most pronounced near the dislocation core and decay slowly as the strain field of the dislocation decreases with distance. We have calculated local moments using the locally self-consistent multiple scattering (LSMS) method for a supercell containing a screw-dislocation quadrupole. Finite size effects are found to be significant indicating that dislocation cores affect the electronic structure and magnetic moments of neighboring dislocations. The influence of neighboring dislocations points to a need to study individual dislocations from first principles just as they appear amid surrounding atoms in large-scale classical force field simulations. An approach for the use of the LSMS to calculate local moments in subvolumes of large atomic configurations generated in the course of classical molecular dynamics simulation of dislocation dynamics is discussed. VC2011 American Institute of Physics. [doi:10.1063/1.3562217
Nagabalasubramanian, P B; Periandy, S; Karabacak, Mehmet; Govindarajan, M
2015-06-15
The solid phase FT-IR and FT-Raman spectra of 4-vinylcyclohexene (abbreviated as 4-VCH) have been recorded in the region 4000-100cm(-1). The optimized molecular geometry and vibrational frequencies of the fundamental modes of 4-VCH have been precisely assigned and analyzed with the aid of structure optimizations and normal coordinate force field calculations based on density functional theory (DFT) method at 6-311++G(d,p) level basis set. The theoretical frequencies were properly scaled and compared with experimentally obtained FT-IR and FT-Raman spectra. Also, the effect due the substitution of vinyl group on the ring vibrational frequencies was analyzed and a detailed interpretation of the vibrational spectra of this compound has been made on the basis of the calculated total energy distribution (TED). The time dependent DFT (TD-DFT) method was employed to predict its electronic properties, such as electronic transitions by UV-Visible analysis, HOMO and LUMO energies, molecular electrostatic potential (MEP) and various global reactivity and selectivity descriptors (chemical hardness, chemical potential, softness, electrophilicity index). Stability of the molecule arising from hyper conjugative interaction, charge delocalization has been analyzed using natural bond orbital (NBO) analysis. Atomic charges obtained by Mulliken population analysis and NBO analysis are compared. Thermodynamic properties (heat capacity, entropy and enthalpy) of the title compound at different temperatures are also calculated.
Theoretical calculations on structural and electronic properties of BGaAsBi alloys
Aslan, Metin; Yalcin, Battal G.; Ustundag, Mehmet; Bagci, Sadik
2015-11-01
The structural and electronic properties of cubic B x Ga1- x As1- y Bi y alloys with bismuth (Bi) concentration of 0.0625, 0.125, 0.1875 and 0.25 are studied with various boron (B) compositions by means of density functional theory (DFT) within the Wu-Cohen (WC) exchange correlation potential based on generalized gradient approximation (GGA). For all studied alloy structures, we have implemented geometric optimization before the volume optimization calculations. The obtained equilibrium lattice constants and band gap of studied quaternary alloys are investigated for the first time in literature. While the lattice constant behavior changes linearly with boron concentration, increasing small amount of bismuth concentration alter the lattice constant nonlinearly. The present calculation shows that the band gap decreases with increasing bismuth concentration and direct band gap semiconductor alloy became an indirect band gap with increasing boron concentration. From the band offset calculation we have shown that increasing B and Bi concentration in host GaAs reduced the valance band offset in a heterostructure formed by GaAs and studied alloys.
Seiler, Christian
2016-01-01
A formalism for electronic-structure calculations is presented that is based on the functional renormalization group (FRG). The traditional FRG has been formulated for systems that exhibit a translational symmetry with an associated Fermi surface, which can provide the organization principle for the renormalization group (RG) procedure. We here advance an alternative formulation, where the RG-flow is organized in the energy-domain rather than in k-space. This has the advantage that it can also be applied to inhomogeneous matter lacking a band-structure, such as disordered metals or molecules. The energy-domain FRG ({\\epsilon}FRG) presented here accounts for Fermi-liquid corrections to quasi-particle energies and particle-hole excitations. It goes beyond the state of the art GW-BSE, because in {\\epsilon}FRG the Bethe-Salpeter equation (BSE) is solved in a self-consistent manner. An efficient implementation of the approach that has been tested against exact diagonalization calculations and calculations based on...
Time domain numerical calculations of the short electron bunch wakefields in resistive structures
Energy Technology Data Exchange (ETDEWEB)
Tsakanian, Andranik
2010-10-15
The acceleration of electron bunches with very small longitudinal and transverse phase space volume is one of the most actual challenges for the future International Linear Collider and high brightness X-Ray Free Electron Lasers. The exact knowledge on the wake fields generated by the ultra-short electron bunches during its interaction with surrounding structures is a very important issue to prevent the beam quality degradation and to optimize the facility performance. The high accuracy time domain numerical calculations play the decisive role in correct evaluation of the wake fields in advanced accelerators. The thesis is devoted to the development of a new longitudinally dispersion-free 3D hybrid numerical scheme in time domain for wake field calculation of ultra short bunches in structures with walls of finite conductivity. The basic approaches used in the thesis to solve the problem are the following. For materials with high but finite conductivity the model of the plane wave reflection from a conducting half-space is used. It is shown that in the conductive half-space the field components perpendicular to the interface can be neglected. The electric tangential component on the surface contributes to the tangential magnetic field in the lossless area just before the boundary layer. For high conducting media, the task is reduced to 1D electromagnetic problem in metal and the so-called 1D conducting line model can be applied instead of a full 3D space description. Further, a TE/TM (''transverse electric - transverse magnetic'') splitting implicit numerical scheme along with 1D conducting line model is applied to develop a new longitudinally dispersion-free hybrid numerical scheme in the time domain. The stability of the new hybrid numerical scheme in vacuum, conductor and bound cell is studied. The convergence of the new scheme is analyzed by comparison with the well-known analytical solutions. The wakefield calculations for a number of
Brandelik, Andreas
2009-07-01
CALCMIN, an open source Visual Basic program, was implemented in EXCEL™. The program was primarily developed to support geoscientists in their routine task of calculating structural formulae of minerals on the basis of chemical analysis mainly obtained by electron microprobe (EMP) techniques. Calculation programs for various minerals are already included in the form of sub-routines. These routines are arranged in separate modules containing a minimum of code. The architecture of CALCMIN allows the user to easily develop new calculation routines or modify existing routines with little knowledge of programming techniques. By means of a simple mouse-click, the program automatically generates a rudimentary framework of code using the object model of the Visual Basic Editor (VBE). Within this framework simple commands and functions, which are provided by the program, can be used, for example, to perform various normalization procedures or to output the results of the computations. For the clarity of the code, element symbols are used as variables initialized by the program automatically. CALCMIN does not set any boundaries in complexity of the code used, resulting in a wide range of possible applications. Thus, matrix and optimization methods can be included, for instance, to determine end member contents for subsequent thermodynamic calculations. Diverse input procedures are provided, such as the automated read-in of output files created by the EMP. Furthermore, a subsequent filter routine enables the user to extract specific analyses in order to use them for a corresponding calculation routine. An event-driven, interactive operating mode was selected for easy application of the program. CALCMIN leads the user from the beginning to the end of the calculation process.
Energy Technology Data Exchange (ETDEWEB)
Chauvin, C
2005-11-15
This thesis is devoted to the definition and the implementation of a multi-resolution method to determine the fundamental state of a system composed of nuclei and electrons. In this work, we are interested in the Density Functional Theory (DFT), which allows to express the Hamiltonian operator with the electronic density only, by a Coulomb potential and a non-linear potential. This operator acts on orbitals, which are solutions of the so-called Kohn-Sham equations. Their resolution needs to express orbitals and density on a set of functions owing both physical and numerical properties, as explained in the second chapter. One can hardly satisfy these two properties simultaneously, that is why we are interested in orthogonal and bi-orthogonal wavelets basis, whose properties of interpolation are presented in the third chapter. We present in the fourth chapter three dimensional solvers for the Coulomb's potential, using not only the preconditioning property of wavelets, but also a multigrid algorithm. Determining this potential allows us to solve the self-consistent Kohn-Sham equations, by an algorithm presented in chapter five. The originality of our method consists in the construction of the stiffness matrix, combining a Galerkin formulation and a collocation scheme. We analyse the approximation properties of this method in case of linear Hamiltonian, such as harmonic oscillator and hydrogen, and present convergence results of the DFT for small electrons. Finally we show how orbital compression reduces considerably the number of coefficients to keep, while preserving a good accuracy of the fundamental energy. (author)
Ab initio calculation of structural stability, electronic and optical properties of Ag{sub 2}Se
Energy Technology Data Exchange (ETDEWEB)
Rameshkumar, S.; Jayalakshmi, V., E-mail: karthikajayam@yahoo.co.in [Department of Physics, SRM University, Ramapuram Campus, Chennai – 600089 (India); Jaiganesh, G. [Materials Science Group, Indira Gandhi Centre for Atomic Research, Kalpakkam – 603102 (India); Palanivel, B. [Department of Physics, Pondicherry Engineering College, Puducherry – 605014 (India)
2015-06-24
The structural stability, electronic and optical properties of Ag{sub 2}Se compound is studied using ab initio packages. Ag{sub 2}Se is found to crystallize in orthorhombic structure with two different space groups i.e. P2{sub 1}2{sub 1}2{sub 1} (No. 19) and P222{sub 1} (No. 17). For this compound in these two space groups, the total energy has been computed as a function of volume. Our calculated results suggest that the P2{sub 1}2{sub 1}2{sub 1}–phase is more stable than that of the P222{sub 1}–phase. The band structure calculation show that Ag{sub 2}Se is semimetallic with an overlap of about 0.014 eV in P2{sub 1}2{sub 1}2{sub 1}–phase whereas is metallic in nature in P222{sub 1}–phase. Moreover, the optical properties including the dielectric function, energy loss spectrum are obtained and analysed.
Model creation and electronic structure calculation of amorphous hydrogenated boron carbide
Belhadj Larbi, Mohammed
Boron-rich solids are of great interest for many applications, particularly, amorphous hydrogenated boron carbide (a-BC:H) thin films are a leading candidate for numerous applications such as: heterostructure materials, neutron detectors, and photovoltaic energy conversion. Despite this importance, the local structural properties of these materials are not well-known, and very few theoretical studies for this family of disordered solids exist in the literature. In order to optimize this material for its potential applications the structure property relationships need to be discovered. We use a hybrid method in this endeavor---which is to the best of our knowledge the first in the literature---to model and calculate the electronic structure of amorphous hydrogenated boron carbide (a-BC:H). A combination of classical molecular dynamics using the Large-scale Atomic/Molecular Massively Parallel Simulator (LAMMPS) and ab initio quantum mechanical simulations using the Vienna ab initio simulation package (VASP) have been conducted to create geometry optimized models that consist of a disordered hydrogenated twelve-vertex boron carbide icosahedra, with hydrogenated carbon cross-linkers. Then, the density functional theory (DFT) based orthogonalized linear combination of atomic orbitals (OLCAO) method was used to calculate the total and partial density of states (TDOS, PDOS), the complex dielectric function epsilon, and the radial pair distribution function (RPDF). The RPDF data stand as predictions that may be compared with future experimental electron or neutron diffraction data. The electronic structure simulations were not able to demonstrate a band gap of the same nature as that seen in prior experimental work, a general trend of the composition-properties relationship was established. The content of hydrogen and boron was found to be directly proportional to the decrease in the number of available states near the fermi energy, and inversely proportional to the
Saikia, Nabanita; Pati, Swapan K.; Deka, Ramesh C.
2012-09-01
One-dimensional nanostructures such as nanowires and nanotubes are stimulating tremendous research interest due to their structural, electronic and magnetic properties. We perform first principles calculation using density functional theory on the structural, and electronics properties of BNNTs adsorbed with isoniazid (INH) drug via noncovalent functionalization using the GGA/PBE functional and DZP basis set implemented in SIESTA program. The band structure, density of states and projected density of states (PDOS) plots suggest that isoniazid prefers to get adsorbed at the hollow site in case of (5,5) BNNT, whereas in (10,0) BNNT it favours the bridge site. The adsorption energy of INH onto (5,5) BNNT is smaller than in (10,0) BNNT which proposes that (10,0) BNNT with a larger radius compared to (5,5) BNNT is more favourable for INH adsorption as the corresponding distortion energy will also be quite lower. Functionalization of (5,5) and (10,0) BNNTs with isoniazid displays the presence of new impurity states (dispersionless bands) within the HOMO-LUMO energy gap of pristine BNNT leading to an increase in reactivity of the INH/BNNT system and lowering of the energy gap of the BNNTs. The PDOS plots show the major contribution towards the dispersionless impurity states is from INH molecule itself rather than from BNNT near the Fermi energy region. To summarize, noncovalent functionalization of BNNTs with isoniazid drug modulates the electronic properties of the pristine BNNT by lowering its energy gap with respect to the Fermi level, as well as demonstrating the preferential site selectivity for adsorption of isoniazid onto the nanotube sidewalls of varying chirality.
Energy Technology Data Exchange (ETDEWEB)
Lin, Lin; Chen, Mohan; Yang, Chao; He, Lixin
2012-02-10
We describe how to apply the recently developed pole expansion plus selected inversion (PEpSI) technique to Kohn-Sham density function theory (DFT) electronic structure calculations that are based on atomic orbital discretization. We give analytic expressions for evaluating charge density, total energy, Helmholtz free energy and atomic forces without using the eigenvalues and eigenvectors of the Kohn-Sham Hamiltonian. We also show how to update the chemical potential without using Kohn-Sham eigenvalues. The advantage of using PEpSI is that it has a much lower computational complexity than that associated with the matrix diagonalization procedure. We demonstrate the performance gain by comparing the timing of PEpSI with that of diagonalization on insulating and metallic nanotubes. For these quasi-1D systems, the complexity of PEpSI is linear with respect to the number of atoms. This linear scaling can be observed in our computational experiments when the number of atoms in a nanotube is larger than a few hundreds. Both the wall clock time and the memory requirement of PEpSI is modest. This makes it even possible to perform Kohn-Sham DFT calculations for 10,000-atom nanotubes on a single processor. We also show that the use of PEpSI does not lead to loss of accuracy required in a practical DFT calculation.
Belyakov, Alexander V.; Nikolaenko, Kirill O.; Davidovich, Pavel B.; Ivanov, Anatolii D.; Garabadzhiu, Alexander V.; Rykov, Anatolii N.; Shishkov, Igor F.
2017-03-01
The molecular structure of isatin, indole-2,3-dione, was studied by gas-phase electron diffraction (GED) and quantum chemical calculations (M062X and MP2 methods with aug-cc-pVTZ basis set). The best fit of the experimental scattering intensities (R-factor = 4.4%) was obtained for a molecular model of Cs symmetry. The structure of the benzene ring deviates from a regular hexagon due to the adjacent pyrrole heterocycle. The small differences between similar geometric parameters were constrained at the values calculated at the M062X level. The experimental structural parameters agree well with the results of theoretical calculations. The bonds in the benzene moiety are in agreement with their standard values. The (Odbnd)Csbnd C(dbnd O) carbon-carbon bond of the pyrrole moiety (1.573(7) Å) is remarkably lengthened in comparison with standard C(sp2)sbnd C(sp2) value, 1.425(11) Å for N-methylpyrrole. According to NBO analysis of isatin, glyoxal and pyrrole-2,3-dione molecules this lengthening cannot be attributed to the steric interactions of Cdbnd O bonds alone and is, mainly, due to the electrostatic repulsion and hyperconjugation that is delocalization of oxygen lone pairs of π-type into the corresponding carbon-carbon antibonding orbital, nπ(O) → σ∗(Csbnd C). Deletion of σ∗(Csbnd C) orbital followed by subsequent geometry optimization led to shortening of the corresponding Csbnd C bond by 0.06 Å. According to different aromaticity descriptors, aromaticity of benzene moiety of isatin is smaller in comparison with benzene molecule. External magnetic field induces diatropic ring current in benzene moiety of isatin.
Grant, Daniel J.; Dixon, David A.; Kemeny, Andre E.; Francisco, Joseph S.
2008-04-01
High level ab initio electronic structure calculations using the coupled cluster CCSD(T) method with augmented correlation-consistent basis sets extrapolated to the complete basis set limit have been performed on the PNO, NOP, and NPO isomers and their corresponding anions and cations. Geometries for all species were optimized up through the aug-cc-pV(Q +d)Z level and vibrational frequencies were calculated with the aug-cc-pV(T +d)Z basis set. The most stable of the three isomers is NPO and it is predicted to have a heat of formation of 23.3kcal/mol. PNO is predicted to be only 1.7kcal/mol higher in energy. The calculated adiabatic ionization potential of NPO is 12.07eV and the calculated adiabatic electron affinity is 2.34eV. The calculated adiabatic ionization potential of PNO is 10.27eV and the calculated adiabatic electron affinity is only 0.24eV. NOP is predicted to be much higher in energy by 29.9kcal/mol. The calculated rotational constants for PNO and NPO should allow for these species to be spectroscopically distinguished. The adiabatic bond dissociation energies for the P N, P O, and N O bonds in NPO and PNO are the same within ˜10kcal/mol and fall in the range of 72-83kcal/mol.
Institute of Scientific and Technical Information of China (English)
Ye Xiao-Qiu; Luo De-Li; Sang Ge; Ao Bing-Yun
2011-01-01
The alanates (complex aluminohydrides) have relatively high gravimetric hydrogen densities and are among the most promising solid-state hydrogen-storage materials. In this work, the electronic structures and the formation enthalpies of seven typical aluminum-based deuterides have been calculated by the plane-wave pseudopotential method,these being AID3, LiAID4, Li3AID6, BaAID5, Ba2AID7, LiMg(AID4)3 and LiMgAID6. The results show that all these compounds are large band gap insulators at 0 K with estimated band gaps from 2.31 eV in AID3 to 4.96 eV in LiMg(AID4)3. The band gaps are reduced when the coordination of Al varies from 4 to 6. Two peaks present in the valence bands are the common characteristics of aluminum-based deuterides containing AID4 subunits while three peaks are the common characteristics of those containing AID6 subunits. The electronic structures of these compounds are determined mainly by aluminum deuteride complexes (AID4 or AID6) and their mutual interactions. The predicted formation enthalpies are presented for the studied aluminum-based deuterides.
GPAW - massively parallel electronic structure calculations with Python-based software.
Energy Technology Data Exchange (ETDEWEB)
Enkovaara, J.; Romero, N.; Shende, S.; Mortensen, J. (LCF)
2011-01-01
Electronic structure calculations are a widely used tool in materials science and large consumer of supercomputing resources. Traditionally, the software packages for these kind of simulations have been implemented in compiled languages, where Fortran in its different versions has been the most popular choice. While dynamic, interpreted languages, such as Python, can increase the effciency of programmer, they cannot compete directly with the raw performance of compiled languages. However, by using an interpreted language together with a compiled language, it is possible to have most of the productivity enhancing features together with a good numerical performance. We have used this approach in implementing an electronic structure simulation software GPAW using the combination of Python and C programming languages. While the chosen approach works well in standard workstations and Unix environments, massively parallel supercomputing systems can present some challenges in porting, debugging and profiling the software. In this paper we describe some details of the implementation and discuss the advantages and challenges of the combined Python/C approach. We show that despite the challenges it is possible to obtain good numerical performance and good parallel scalability with Python based software.
Energy Technology Data Exchange (ETDEWEB)
Yuan, H. K.; Chen, H., E-mail: chenh@swu.edu.cn; Tian, C. L.; Kuang, A. L.; Wang, J. Z. [School of Physical Science and Technology, Southwest University, Chongqing 400715 (China)
2014-04-21
Gadolinium-oxide clusters in various sizes and stoichiometries have been systematically studied by employing the density functional theory with the generalized gradient approximation. The clusters in bulk stoichiometry are relatively more stable and their binding energies increase with the increasing size. Stoichiometric (Gd{sub 2}O{sub 3}){sub n} clusters of n = 1–3 prefer cage-like structures, whereas the clusters of n = 4–30 prefer compact structures layered by wedge-like units and exhibit a rough feature toward the bulk-like arrangement with small disorders of atomic positions. The polyhedral-cages analogous to carbon-fullerenes are stable isomers yet not the minimum energy configurations. Their stabilities can be improved by embedding one oxygen atom or a suitable cage to form core-shell configurations. The mostly favored antiferromagnetic couplings between adjacent Gd atoms are nearly degenerated in energy with their ferromagnetic couplings, resulting in super-paramagnetic characters of gadolinium-oxide clusters. The Ruderman-Kittel-Kasuya-Yosida (RKKY)-type mechanism together with the superexchange-type mechanism plays cooperation role for the magnetic interactions in clusters. We present, as a function of n, calculated binding energies, ionization potential, electron affinity, and electronic dipole moment.
Electronic Structure of Aromatic and Quinoidic Oligothiophenes by First-principles Calculations
Mizuseki, Hiroshi; Kawazoe, Yoshiyuki
2009-03-01
Since the discovery in 1977 that trans-polyacetylene can be made electrically conducting by means of doping[1] several different conjugated polymers with interesting properties in the conducting and semiconducting phases have been discovered. Polythiophene has a typical π-conjugated system, then many polythiophenes are synthesized and several have been well characterized. Calculation systems based on neutral, doubly charged, and highly charged oligomers whose all ring are linked to have linear chains were studied as model for the polaronic defects in doped polythiophenes. The energetics of the aromatic and quinoid structures is investigated using the both ends of neutral oligomers substituted by dimethyl and dimethylen. To estimate the electronic structures, the difference between corresponding bond lengths along the C-C path of neutral, dicationic, and dianionic oligomers, were investigated. Calculations were performed on systems containing 16 monomers, by using B3LYP/6-31G(d) level of theory. References [1] C. K. Chiang et al., Phys. Rev. Lett. 39, 1098 (1977). [2] http://www-lab.imr.edu/˜mizuseki/nanowire.html
Institute of Scientific and Technical Information of China (English)
无
2009-01-01
The valence electronic structures of Fe, Co and Ni have been investigated with Empirical Electron Theory of Solids and Molecules. The magnetic moments, Curie temperature, cohesive energy and melting point have been calculated according to the valence electronic structure. These calculations fit the experimental data very well. Based on the calculations, the magnetic moments are proportional to the number of 3d magnetic electrons. Curie temperatures are related to the magnetic electrons and the bond lengths between magnetic atoms. Cohesive energies increase with the increase of the number of covalent electrons, and the decrease of the number of magnetic and dumb pair electrons. The melting point is mainly related to the number of covalent electron pairs distributed in the strongest bond. The contribution from the lattice electrons is very small, the dumb pair electrons weaken the melting point; however, the contribution to melting point of the magnetic electrons can be neglected. It reveals that the magnetic and thermal properties are closely related to the valence electronic structures, and the changes or transitions between the electrons obviously affect the physical properties.
Institute of Scientific and Technical Information of China (English)
WU WenXia; XUE ZhiYong; HONG Xing; LI XiuMei; GUO YongQuan
2009-01-01
The valence electronic structures of Fe, Co and Ni have been investigated with Empirical Electron Theory of Solids and Molecules. The magnetic moments, Curie temperature, cohesive energy and melting point have been calculated according to the valence electronic structure. These calculations fit the experimental data very well. Based on the calculations, the magnetic moments are proportional to the number of 3d magnetic electrons. Curie temperatures are related to the magnetic electrons and the bond lengths between magnetic atoms. Cohesive energies increase with the increase of the number of covalent electrons, and the decrease of the number of magnetic and dumb pair electrons. The melting point is mainly related to the number of covalent electron pairs distributed in the strongest bond. The contribution from the lattice electrons is very small, the dumb pair electrons weaken the melting point; however, the contribution to melting point of the magnetic electrons can be neglected. It reveals that the magnetic and thermal properties are closely related to the valence electronic structures, and the changes or transitions between the electrons obviously affect the physical properties.
Energy Technology Data Exchange (ETDEWEB)
Hinsche, Nicki; Yavorski, Bogdan; Zahn, Peter; Mertig, Ingrid [Martin-Luther-Universitaet, Institut fuer Physik, Halle/S. (Germany)
2010-07-01
Starting from bulk silicon, we studied the valley splitting due to symmetry breaking that occurs in rolled-up Si. Valley splitting in Si was studied recently because of tetragonal distortion and quantum well effects in heterostructures. The new aspect in nowadays experimentally accessible rolled-up Si tubes is that symmetry breaking occurs in all spatial directions. As a result, splitting of the six-fold degenerate conduction-band minimum is expected to be lifted. This has a strong influence on the transport properties as well. In detail, the anisotropy of the effective masses of charge carriers contributing to the conductivity in different directions are studied in dependence on the applied strain. The electronic structure is calculated self consistently within the framework of density functional theory. The transport properties of the promising thermoelectric material are studied in the diffusive limit of transport applying the Boltzmann theory in relaxation time approximation.
Yelgel, Celal
2016-04-01
We present an extensive density functional theory (DFT) based investigation of the electronic structures of ABC-stacked N-layer graphene. It is found that for such systems the dispersion relations of the highest valence and the lowest conduction bands near the K point in the Brillouin zone are characterised by a mixture of cubic, parabolic, and linear behaviours. When the number of graphene layers is increased to more than three, the separation between the valence and conduction bands decreases up until they touch each other. For five and six layer samples these bands show flat behaviour close to the K point. We note that all states in the vicinity of the Fermi energy are surface states originated from the top and/or bottom surface of all the systems considered. For the trilayer system, N = 3, pronounced trigonal warping of the bands slightly above the Fermi level is directly obtained from DFT calculations.
Electronic Structure Calculations and Adaptation Scheme in Multi-core Computing Environments
Energy Technology Data Exchange (ETDEWEB)
Seshagiri, Lakshminarasimhan; Sosonkina, Masha; Zhang, Zhao
2009-05-20
Multi-core processing environments have become the norm in the generic computing environment and are being considered for adding an extra dimension to the execution of any application. The T2 Niagara processor is a very unique environment where it consists of eight cores having a capability of running eight threads simultaneously in each of the cores. Applications like General Atomic and Molecular Electronic Structure (GAMESS), used for ab-initio molecular quantum chemistry calculations, can be good indicators of the performance of such machines and would be a guideline for both hardware designers and application programmers. In this paper we try to benchmark the GAMESS performance on a T2 Niagara processor for a couple of molecules. We also show the suitability of using a middleware based adaptation algorithm on GAMESS on such a multi-core environment.
An approach to first principles electronic structure calculation by symbolic-numeric computation
Directory of Open Access Journals (Sweden)
Akihito Kikuchi
2013-04-01
Full Text Available There is a wide variety of electronic structure calculation cooperating with symbolic computation. The main purpose of the latter is to play an auxiliary role (but not without importance to the former. In the field of quantum physics [1-9], researchers sometimes have to handle complicated mathematical expressions, whose derivation seems almost beyond human power. Thus one resorts to the intensive use of computers, namely, symbolic computation [10-16]. Examples of this can be seen in various topics: atomic energy levels, molecular dynamics, molecular energy and spectra, collision and scattering, lattice spin models and so on [16]. How to obtain molecular integrals analytically or how to manipulate complex formulas in many body interactions, is one such problem. In the former, when one uses special atomic basis for a specific purpose, to express the integrals by the combination of already known analytic functions, may sometimes be very difficult. In the latter, one must rearrange a number of creation and annihilation operators in a suitable order and calculate the analytical expectation value. It is usual that a quantitative and massive computation follows a symbolic one; for the convenience of the numerical computation, it is necessary to reduce a complicated analytic expression into a tractable and computable form. This is the main motive for the introduction of the symbolic computation as a forerunner of the numerical one and their collaboration has won considerable successes. The present work should be classified as one such trial. Meanwhile, the use of symbolic computation in the present work is not limited to indirect and auxiliary part to the numerical computation. The present work can be applicable to a direct and quantitative estimation of the electronic structure, skipping conventional computational methods.
Imachi, Hiroto; Yokoyama, Seiya; Kaji, Takami; Abe, Yukiya; Tada, Tomofumi; Hoshi, Takeo
2016-12-01
One-hundred-nm-scale electronic structure calculations were carried out on the K supercomputer by our original simulation code ELSES (http://www.elses.jp/) The present paper reports preliminary results of transport calculations for condensed organic polymers. Large-scale calculations are realized by novel massively parallel order-N algorithms. The transport calculations were carried out as a theoretical extension for the quantum wavepacket dynamics simulation. The method was applied to a single polymer chain and condensed polymers.
Electronic structure, rovibrational, and dipole moment calculations for the AsCl molecule.
Mourad, Khaled A; Abdulal, Saleh N; Korek, Mahmoud
2016-02-01
The potential energy curves of the 19 lowest-lying singlet and triplet electronic states in the (2S+1)Λ((+/-)) representation of the AsCl molecule have been investigated using the complete active space self-consistent field (CASSCF) with multireference configuration interaction (MRCI+Q) method including single and double excitations and with the Davidson correction. The harmonic frequency ω e, the internuclear distance R e, the dipole moment, and the electronic energy with respect to the ground state T e were calculated for the electronic states considered. By using the canonical functions approach, the eigenvalue E v, the rotational constant B v, and the abscissae of the turning points R min and R max were calculated for the electronic states up to the vibrational level v = 60. The values obtained in the present work agree well with corresponding values available in the literature for several electronic states. Fifteen new electronic states were investigated here for the first time.
Energy Technology Data Exchange (ETDEWEB)
Piskunov, Sergei, E-mail: piskunov@lu.l [Faculty of Computing, University of Latvia, 19 Raina blvd., Riga LV-1586 (Latvia); Faculty of Physics and Mathematics, University of Latvia, 8 Zellu Str., Riga LV-1002 (Latvia); Zvejnieks, Guntars; Zhukovskii, Yuri F. [Institute for Solid State Physics, University of Latvia, 8 Kengaraga Str., LV-1063, Riga (Latvia); Bellucci, Stefano [INFN-Laboratori Nazionali di Frascati, Via Enrico Fermi 40, I-00044, Frascati (Italy)
2011-03-31
In this study, we perform first principles simulations on both atomically smooth and nanostructured Ni(111) slabs. The latter contains periodically distributed nickel nanoclusters atop a thin metal film gradually growing from adatoms and serving as a promising catalyst. Applying the generalized gradient approximation within the formalism of the density functional theory we compare the atomic and electronic structures of Ni bulk, as well as both perfect and nanostructured (111) surfaces obtained using two different ab initio approaches: (i) the linear combination of atomic orbitals and (ii) the projector augmented plane waves. The most essential inter-atomic forces between the Ni adatoms upon the substrate have been found to be formed via: (i) attractive pair-wise interactions, (ii) repulsive triple-wise interactions within a triangle and (iii) attractive triple-wise interactions within a line between the nearest adatoms. The attractive interactions surmount the repulsive forces, hence resulting in the formation of stable clusters from Ni adatoms. The magnetic moment and the effective charge (within both Mulliken and Bader approaches) of the outer atoms in Ni nanoparticles increase as compared to those for the smooth Ni(111) surface. The calculated electronic charge redistribution in the Ni nanoclusters features them as possible adsorption centers with increasing catalytic activity, e.g., for further synthesis of carbon nanotubes.
Briggs, Emil; Hodak, Miroslav; Lu, Wenchang; Bernholc, Jerry; Li, Yan
RMG is a cross platform open source package for ab initio electronic structure calculations that uses real-space grids, multigrid pre-conditioning, and subspace diagonalization to solve the Kohn-Sham equations. The code has been successfully used for a wide range of problems ranging from complex bulk materials to multifunctional electronic devices and biological systems. RMG makes efficient use of GPU accelerators, if present, but does not require them. Recent work has extended GPU support to systems with multiple GPU's per computational node, as well as optimized both CPU and GPU memory usage to enable large problem sizes, which are no longer limited by the memory of the GPU board. Additional enhancements include increased portability, scalability and performance. New versions of the code are regularly released at sourceforge.net/projects/rmgdft/. The releases include binaries for Linux, Windows and MacIntosh systems, automated builds for clusters using cmake, as well as versions adapted to the major supercomputing installations and platforms.
Bringing about matrix sparsity in linear-scaling electronic structure calculations.
Rubensson, Emanuel H; Rudberg, Elias
2011-05-01
The performance of linear-scaling electronic structure calculations depends critically on matrix sparsity. This article gives an overview of different strategies for removal of small matrix elements, with emphasis on schemes that allow for rigorous control of errors. In particular, a novel scheme is proposed that has significantly smaller computational overhead compared with the Euclidean norm-based truncation scheme of Rubensson et al. (J Comput Chem 2009, 30, 974) while still achieving the desired asymptotic behavior required for linear scaling. Small matrix elements are removed while ensuring that the Euclidean norm of the error matrix stays below a desired value, so that the resulting error in the occupied subspace can be controlled. The efficiency of the new scheme is investigated in benchmark calculations for water clusters including up to 6523 water molecules. Furthermore, the foundation of matrix sparsity is investigated. This includes a study of the decay of matrix element magnitude with distance between basis function centers for different molecular systems and different methods. The studied methods include Hartree–Fock and density functional theory using both pure and hybrid functionals. The relation between band gap and decay properties of the density matrix is also discussed.
Calculated Electronic and Magnetic Structure of Screw Dislocations in Alpha Iron
Energy Technology Data Exchange (ETDEWEB)
Odbadrakh, Khorgolkhuu [ORNL; Rusanu, Aurelian [ORNL; Stocks, George Malcolm [ORNL; Samolyuk, German D [ORNL; Eisenbach, Markus [ORNL; Wang, Yang [Pittsburgh Supercomputing Center; Nicholson, Don M [ORNL
2011-01-01
Local atomic magnetic moments in crystalline Fe are perturbed by the presence of dislocations. The effects are most pronounced near the dislocation core and decay slowly as the strain field of the dislocation decreases with distance. We have calculated the local moments using the Locally Self-consistent Multiple Scattering (LSMS) method for an 1848 atom supercell containing a screw- dislocation quadrupole. The atomic positions were determined by relaxation with an embedded atom force field. Finite size effects are found to be significant for this small cell size indicating that dislocation cores affect the electronic structure and magnetic moments of neighboring dislocations. The influence of neighboring dislocations point to a need to study individual dislocations from first principles just as they appear amidst surrounding atoms in large scale classical force field simulations. An approach for the use of the LSMS to calculate local moments in sub-volumes of large atomic configurations generated in the course of classical MD simulation of dislocation dynamics is discussed.
Institute of Scientific and Technical Information of China (English)
LIU Zhilin; LIN Cheng; LIU Yan; GUO Yanchang
2005-01-01
Combined with the phase transformations in rolling, the phase configuration, the tensile strength, and the yield strength with different terminal rolling grain sizes in Q235 strip steel have been theoretically calculated using the covalent electron number (nA) of the strongest bond in phase cells and the interface electron density difference (Ap) in alloys. The calculated results agree well with the results of real production. Therefore, the calculation method of terminal rolling tensile and yield strength in the non-quenched-tempered steel containing pearlite is given by the alloying electron structure parameters.
Directory of Open Access Journals (Sweden)
Lihua Xiao
2011-06-01
Full Text Available The electronic structure and the optical performance of YB6 were investigated by first-principles calculations within the framework of density functional theory. It was found that the calculated results are in agreement with the relevant experimental data. Our theoretical studies showed that YB6 is a promising solar radiation shielding material for windows.
Electronic structure of O-doped SiGe calculated by DFT + U method
Zhao, Zong-Yan; Yang, Wen; Yang, Pei-Zhi
2016-12-01
To more in depth understand the doping effects of oxygen on SiGe alloys, both the micro-structure and properties of O-doped SiGe (including: bulk, (001) surface, and (110) surface) are calculated by DFT + U method in the present work. The calculated results are as follows. (i) The (110) surface is the main exposing surface of SiGe, in which O impurity prefers to occupy the surface vacancy sites. (ii) For O interstitial doping on SiGe (110) surface, the existences of energy states caused by O doping in the band gap not only enhance the infrared light absorption, but also improve the behaviors of photo-generated carriers. (iii) The finding about decreased surface work function of O-doped SiGe (110) surface can confirm previous experimental observations. (iv) In all cases, O doing mainly induces the electronic structures near the band gap to vary, but is not directly involved in these variations. Therefore, these findings in the present work not only can provide further explanation and analysis for the corresponding underlying mechanism for some of the experimental findings reported in the literature, but also conduce to the development of μc-SiGe-based solar cells in the future. Project supported by the Natural Science Foundation of Yunnan Province, China (Grant No. 2015FB123), the 18th Yunnan Province Young Academic and Technical Leaders Reserve Talent Project, China (Grant No. 2015HB015), and the National Natural Science Foundation of China (Grant No. U1037604).
Luo, D.; Pradhan, A. K.
1990-01-01
The new R-matrix package for comprehensive close-coupling calculations for electron scattering with the first three ions in the boron isoelectronic sequence, the astrophysically significant C(+), N(2+), and O(3+), is presented. The collision strengths are calculated in the LS coupling approximation, as well as in pair-coupling scheme, for the transitions among the fine-structure sublevels. Calculations are carried out at a large number of energies in order to study the detailed effects of autoionizing resonances.
Energy Technology Data Exchange (ETDEWEB)
Lin, Lin; Yang, Chao; Lu, Jiangfeng; Ying, Lexing; E, Weinan
2009-09-25
We present an efficient parallel algorithm and its implementation for computing the diagonal of $H^-1$ where $H$ is a 2D Kohn-Sham Hamiltonian discretized on a rectangular domain using a standard second order finite difference scheme. This type of calculation can be used to obtain an accurate approximation to the diagonal of a Fermi-Dirac function of $H$ through a recently developed pole-expansion technique \\cite{LinLuYingE2009}. The diagonal elements are needed in electronic structure calculations for quantum mechanical systems \\citeHohenbergKohn1964, KohnSham 1965,DreizlerGross1990. We show how elimination tree is used to organize the parallel computation and how synchronization overhead is reduced by passing data level by level along this tree using the technique of local buffers and relative indices. We analyze the performance of our implementation by examining its load balance and communication overhead. We show that our implementation exhibits an excellent weak scaling on a large-scale high performance distributed parallel machine. When compared with standard approach for evaluating the diagonal a Fermi-Dirac function of a Kohn-Sham Hamiltonian associated a 2D electron quantum dot, the new pole-expansion technique that uses our algorithm to compute the diagonal of $(H-z_i I)^-1$ for a small number of poles $z_i$ is much faster, especially when the quantum dot contains many electrons.
Dirac-Fock atomic electronic structure calculations using different nuclear charge distributions
Visscher, L; Dyall, KG
1997-01-01
Numerical Hartree-Fock calculations based on the Dirac-Coulomb Hamiltonian for the first 109 elements of the periodic table are presented. The results give the total electronic energy, as a function of the nuclear model that is used, for four different models of the nuclear charge distribution. The
Imachi, Hiroto
2015-01-01
Optimally hybrid numerical solvers were constructed for massively parallel generalized eigenvalue problem (GEP).The strong scaling benchmark was carried out on the K computer and other supercomputers for electronic structure calculation problems in the matrix sizes of M = 10^4-10^6 with upto 105 cores. The procedure of GEP is decomposed into the two subprocedures of the reducer to the standard eigenvalue problem (SEP) and the solver of SEP. A hybrid solver is constructed, when a routine is chosen for each subprocedure from the three parallel solver libraries of ScaLAPACK, ELPA and EigenExa. The hybrid solvers with the two newer libraries, ELPA and EigenExa, give better benchmark results than the conventional ScaLAPACK library. The detailed analysis on the results implies that the reducer can be a bottleneck in next-generation (exa-scale) supercomputers, which indicates the guidance for future research. The code was developed as a middleware and a mini-application and will appear online.
Khadraoui, Z.; Horchani-Naifer, K.; Ferhi, M.; Ferid, M.
2015-09-01
Single crystals of TbPO4 were grown by high temperature solid-state reaction and identified by means of X-ray diffraction, infrared and Raman spectroscopies analysis. The electronic properties of TbPO4 such as the energy band structures, density of states were carried out using density functional theory (DFT). We have employed the LDA+U functional to treat the exchange correlation potential by solving Kohn-Sham equation. The calculated total and partial density of states indicate that the top of valance band is mainly built upon O-2p states and the bottom of the conduction band mostly originates from Tb-5d states. The population analysis indicates that the P-O bond was mainly covalent and Tb-O bond was mainly ionic. The emission spectrum, color coordinates and decay curve were employed to reveal the luminescence properties of TbPO4. Moreover, the optical properties including the dielectric function, absorption spectrum, refractive index, extinction coefficient, reflectivity and energy-loss spectrum are investigated and analyzed. The results are discussed and compared with the available experimental data.
Energy Technology Data Exchange (ETDEWEB)
Wu, Hai-Ying; Zhou, Ping; Han, Xiang-Yu [Jiaotong Univ., Chongqing (China). School of Science; Chen, Ya-Hong [North Univ. of China, Taiyuan (China). Scholl of Chemical Engineering and Environment; Liu, Zi-Jiang [Lanzhou City Univ. (China). Dept. of Physics
2014-08-15
The structural, electronic, and mechanical stability properties of magnesium sulfide in different phases are presented using the plane wave pseudopotential method within the generalized gradient approximation. Eight different phases such as rocksalt (B1), zincblende (B3), wurtzite (B4), nickel arsenide (B8), cesium chloride (B2), PH{sub 4}I-type (B11), FeSi-type (B28), and MnP-type (B31) are considered in great detail. The calculated ground-state properties of these phases are consistent with available experimental and theoretical data. It is found that MgS in the B1 and B8 phases are indirect band gap materials, the B3, B4, B11, B28, and B31 phases are all direct gap materials, while the B2 phase displays the metallic character. The B1, B3, B4, B8, B28, and B31 phases are mechanically stable at ambient conditions, but the B2 and B11 phases are mechanically unstable under zero pressure and zero temperature.
Lin, Lin; Yang, Chao; He, Lixin
2012-01-01
We describe how to apply the recently developed pole expansion plus selected inversion (PEpSI) technique to Kohn-Sham density function theory (DFT) electronic structure calculations that are based on atomic orbital discretization. We give analytic expressions for evaluating charge density, total energy, Helmholtz free energy and atomic forces without using the eigenvalues and eigenvectors of the Kohn-Sham Hamiltonian. We also show how to update the chemical potential without using Kohn-Sham eigenvalues. The advantage of using PEpSI is that it has a much lower computational complexity than that associated with the matrix diagonalization procedure. We demonstrate the performance gain by comparing the timing of PEpSI with that of diagonalization on insulating and metallic nanotubes. For these quasi-1D systems, the complexity of PEpSI is linear with respect to the number of atoms. This linear scaling can be observed in our computational experiments when the number of atoms in a nanotube is larger than a few hundr...
El-Kork, Nayla; Abu el kher, Nariman; Korjieh, Farah; Chtay, John Anwar; Korek, Mahmoud
2017-04-01
A theoretical investigation for the feasibility of laser-cooling is performed through the calculation of accurate potential energy curves, static dipole moments, spectroscopic constants and rovibrational calculations for 24, 26 and 27 highly excited electronic states for BeF, CaF and MgF molecules respectively. In order to understand the electronic structure of their lowest lying electronic states and to learn the characteristic behavior of their chemical bonding, a high level of calculation is realized by using the complete active space self-consistent field (CASSCF) with multi-reference configuration interaction MRCI method including single and double excitations with Davidson correction (+ Q) for the three considered molecules. The comparison between the values of the present work and those available in the literature for several electronic states shows a good agreement. Fifty new excited electronic states have been investigated, in the present work, for the first time for the three studied molecules.
El-Kork, Nayla; Abu El Kher, Nariman; Korjieh, Farah; Chtay, John Anwar; Korek, Mahmoud
2017-04-15
A theoretical investigation for the feasibility of laser-cooling is performed through the calculation of accurate potential energy curves, static dipole moments, spectroscopic constants and rovibrational calculations for 24, 26 and 27 highly excited electronic states for BeF, CaF and MgF molecules respectively. In order to understand the electronic structure of their lowest lying electronic states and to learn the characteristic behavior of their chemical bonding, a high level of calculation is realized by using the complete active space self-consistent field (CASSCF) with multi-reference configuration interaction MRCI method including single and double excitations with Davidson correction (+Q) for the three considered molecules. The comparison between the values of the present work and those available in the literature for several electronic states shows a good agreement. Fifty new excited electronic states have been investigated, in the present work, for the first time for the three studied molecules.
Application of Plane Wave Method to the Calculation of Electronic States of Nano-Structures
Institute of Scientific and Technical Information of China (English)
LI Shu-Shen; XIA Jian-Bai
2006-01-01
@@ The electronic states of nano-structures are studied in the framework of effective-mass envelope-function theory using the plane wave basis. The barrier width and the number of plane waves are proposed to be 2.5 times the effective Bohr radius and 15n, respectively, for n-dimensional nano-structures (n = 1, 2, 3). Our proposals can be widely applied in the design of various nano-structure devices.
Energy Technology Data Exchange (ETDEWEB)
Werwiński, M. [Institute of Molecular Physics, Polish Academy of Sciences, Smoluchowskiego 17, 60-179 Poznań (Poland); Szajek, A. [Institute of Molecular Physics, Polish Academy of Sciences, Smoluchowskiego 17, 60-179 Poznań (Poland); Centre for Advanced Materials and Smart Structures, Polish Academy of Sciences, Okólna 2, 50-950 Wrocław (Poland); Ślebarski, A. [Institute of Physics, University of Silesia, Uniwersytecka 4, 40-007 Katowice (Poland); Centre for Advanced Materials and Smart Structures, Polish Academy of Sciences, Okólna 2, 50-950 Wrocław (Poland); Kaczorowski, D., E-mail: D.Kaczorowski@int.pan.wroc.pl [Institute of Low Temperature and Structure Research, Polish Academy of Sciences, P. O. Box 1410, 50-950 Wrocław (Poland); Centre for Advanced Materials and Smart Structures, Polish Academy of Sciences, Okólna 2, 50-950 Wrocław (Poland)
2015-10-25
The electronic structure of a heavy-fermion superconductor Ce{sub 2}PdIn{sub 8} was investigated by means of X-ray photoelectron spectroscopy (XPS) and ab initio density functional band structure calculations. The Ce 3d core-level XPS spectra point to stable trivalent configuration of Ce atoms that is also reproduced in the band structure calculations within the generalized gradient approximation GGA+U approach. Analysis of the 3d{sup 9}f{sup 2} weight in the 3d XPS spectra within the Gunnarsson-Schönhammer model suggests that the onsite hybridization energy between Ce 4f and the conduction band states, Δ{sub fs}, is ∼120 meV, which is about 30 meV larger than Δ{sub fs} in isostructural Ce{sub 2}TIn{sub 8} compounds with T = Co, Rh, and Ir. Taking into account a Coulomb repulsion U on both the Ce 4f and Pd 4d states in electronic band structure calculations, a satisfactory agreement was found between the calculated density of states (DOS) and the measured valence band XPS spectra. - Highlights: • XPS data validated strong electronic correlations in superconducting Ce{sub 2}PdIn{sub 8}. • DFT calculations reproduced XPS spectra measured for Ce{sub 2}PdIn{sub 8}. • Crucial role of Pd d electrons in the HF behavior of Ce{sub 2}PdIn{sub 8} was established.
Lavrentyev, A. A.; Gabrelian, B. V.; Vu, V. T.; Ananchenko, L. N.; Isaenko, L. I.; Yelisseyev, A. P.; Khyzhun, O. Y.
2017-04-01
We report on measurements of X-ray photoelectron (XP) spectra for pristine and Ar+ ion-irradiated surfaces of LiGaSe2 single crystal grown by Bridgman-Stockbarger method. Electronic structure of the LiGaSe2 compound is studied from a theoretical and experimental viewpoint. In particular, total and partial densities of states of LiGaSe2 are investigated by density functional theory (DFT) calculations employing the augmented plane wave + local orbitals (APW + lo) method and they are verified by data of X-ray spectroscopy measurements. The DFT calculations indicate that the main contributors to the valence band of LiGaSe2 are the Se 4p states, which contribute mainly at the top and in the upper portion of the valence band, with also essential contributions of these states in the lower portion of the band. Other substantial contributions to the valence band of LiGaSe2 emerge from the Ga 4s and Ga 4p states contributing mainly at the lower ant upper portions of the valence band, respectively. With respect to the conduction band, the calculations indicate that its bottom is composed mainly from contributions of the unoccupied Ga s and Se p states. The present calculations are confirmed experimentally when comparing the XP valence-band spectrum of the LiGaS2 single crystal on a common energy scale with the X-ray emission bands representing the energy distribution of the Ga 4p and Se 4p states. Measurements of the fundamental absorption edges at room temperature reveal that bandgap value, Eg, of LiGaSe2 is equal to 3.47 eV and the Eg value increases up to 3.66 eV when decreasing temperature to 80 K. The main optical characteristics of the LiGaSe2 compound are clarified by the DFT calculations.
Energy Technology Data Exchange (ETDEWEB)
Kizaki, H., E-mail: hkizaki@aquarius.mp.es.osaka-u.ac.j [Graduate School of Engineering Science, Osaka University, Toyonaka, Osaka 567-8531 (Japan); Toyoda, M.; Sato, K. [The Institute of Scientific and Industrial Research, Osaka University, 8-1 Mihogaoka, Ibaraki, Osaka 567-0047 (Japan); Katayama-Yoshida, H. [Graduate School of Engineering Science, Osaka University, Toyonaka, Osaka 567-8531 (Japan); The Institute of Scientific and Industrial Research, Osaka University, 8-1 Mihogaoka, Ibaraki, Osaka 567-0047 (Japan)
2009-12-15
Electronic structure of TiO{sub 2} (rutile) based dilute magnetic semiconductors (DMS) are investigated within self-interaction-corrected local density approximation (SIC-LDA) from first-principles calculation. These results are compared with those calculated within standard LDA. It is found that the calculated band-gap energy in the host TiO{sub 2} is different within the LDA and the SIC-LDA. We find that high-spin state is predicted within the SIC-LDA with oxygen vacancy. The calculated density of states within SIC-LDA is in good agreement with photoemission results.
Nonrelativistic structure calculations of two-electron ions in a strongly coupled plasma environment
Energy Technology Data Exchange (ETDEWEB)
Bhattacharyya, S.; Saha, J. K.; Mukherjee, T. K.
2015-04-01
In this work, the controversy between the interpretations of recent measurements on dense aluminum plasma created with the Linac coherent light source (LCLS) x-ray free electron laser (FEL) and the Orion laser has been addressed. In both kinds of experiments, heliumlike and hydrogenlike spectral lines are used for plasma diagnostics. However, there exist no precise theoretical calculations for He-like ions within a dense plasma environment. The strong need for an accurate theoretical estimate for spectral properties of He-like ions in a strongly coupled plasma environment leads us to perform ab initio calculations in the framework of the Rayleigh-Ritz variation principle in Hylleraas coordinates where an ion-sphere potential is used. An approach to resolve the long-drawn problem of numerical instability for evaluating two-electron integrals with an extended basis inside a finite domain is presented here. The present values of electron densities corresponding to the disappearance of different spectral lines obtained within the framework of an ion-sphere potential show excellent agreement with Orion laser experiments in Al plasma and with recent theories. Moreover, this method is extended to predict the critical plasma densities at which the spectral lines of H-like and He-like carbon and argon ions disappear. Incidental degeneracy and level-crossing phenomena are being reported for two-electron ions embedded in strongly coupled plasma. Thermodynamic pressure experienced by the ions in their respective ground states inside the ion spheres is also reported.
Energy Technology Data Exchange (ETDEWEB)
Korshunov, Maxim M. [L.V. Kirensky Institute of Physics, Siberian Branch of RAS, Akademgorodok, 660036 Krasnoyarsk (Russian Federation); Max-Planck-Institut fuer Physik komplexer Systeme, Noethnitzer Str. 38, D-01187 Dresden (Germany)], E-mail: maxim@mpipks-dresden.mpg.de; Ovchinnikov, Sergey G. [Max-Planck-Institut fuer Physik komplexer Systeme, Noethnitzer Str. 38, D-01187 Dresden (Germany)
2007-09-01
Mean-field theory of the non-superconducting phase of the high-T{sub c} cuprates is formulated within the effective t-t'-t''-J model with three-site correlated hoppings. This model with the ab initio calculated parameters results from the LDA + GTB method. The static spin and kinematical correlation functions beyond Hubbard I approximation are calculated self-consistently taking into account hoppings to the first, the second, and the third neighboring sites, as well as the three-site correlated hoppings. The obtained Fermi surface evolves from hole-pockets at low-doping to large hole-type Fermi surface at higher doping concentrations. Calculated doping dependence of the nodal Fermi velocity, the effective mass and the chemical potential shift are in good agreement with experimental data.
Energy Technology Data Exchange (ETDEWEB)
Wang, Lin-Wang; Zhao, Zhengji; Meza, Juan; Wang, Lin-Wang
2008-07-11
We present a new linear scaling ab initio total energy electronic structure calculation method based on the divide-and-conquer strategy. This method is simple to implement, easily to parallelize, and produces very accurate results when compared with the direct ab initio method. The method has been tested using up to 8,000 processors, and has been used to calculate nanosystems up to 15,000 atoms.
DEFF Research Database (Denmark)
Romero, N. A.; Glinsvad, Christian; Larsen, Ask Hjorth
2013-01-01
Density function theory (DFT) is the most widely employed electronic structure method because of its favorable scaling with system size and accuracy for a broad range of molecular and condensed-phase systems. The advent of massively parallel supercomputers has enhanced the scientific community's ...
Khaikin, L. S.; Tikhonov, D. S.; Grikina, O. E.; Rykov, A. N.; Stepanov, N. F.
2014-05-01
The equilibrium molecular structure of 2-methyl-1,4-naphthoquinone (vitamin K3) having C s symmetry is experimentally characterized for the first time by means of gas-phase electron diffraction using quantum-chemical calculations and data on the vibrational spectra of related compounds.
Energy Technology Data Exchange (ETDEWEB)
Razee, S.S.A.; Staunton, J.B. [Department of Physics, University of Warwick, Coventry (United Kingdom); Ginatempo, B.; Bruno, E. [Dipartimento di Fisica and Unita INFM, Universita di Messina, Messina (Italy); Pinski, F.J. [Department of Physics, University of Cincinnati, OH (United States)
2001-09-24
A theory is presented for describing the effects of annealing magnetic alloys in magnetic fields. It has an ab initio spin-polarized relativistic Korringa-Kohn-Rostoker coherent potential approximation (KKR-CPA) electronic structure basis and uses the framework of concentration waves. Alloys which would otherwise be soft magnets are found experimentally to develop directional chemical order and significant uniaxial anisotropy when annealed in magnetic fields. Our approach is able to provide a quantitative description of these effects together with the underlying electronic mechanisms. We describe applications to the soft magnetic alloys permalloy and FeCo. (author)
First-principles calculations of the electronic structure of one-dimensional C60 polymers
Beu, Titus A.; Onoe, Jun; Hida, Akira
2005-10-01
The geometrical and electronic properties of two dimers (one with C2h symmetry) from the Stone-Wales rearrangement sequence of C60 dimers [described by E. Osawa and K. Honda, Full Sci. Technol. 4, 939 (1996)] are investigated by density functional and tight-binding calculations. The trimer and the infinite periodic polymer derived from the C2h symmetry dimer are shown to continue a decreasing trend of the energy gap between the highest occupied (HOMO) and the lowest unoccupied (LUMO) molecular orbitals to values smaller than 0.1 eV. The very small energy gap, in conjunction with the extension of the HOMO orbital over the whole cross-linkage region, provides an explanation for the observed conducting properties of electron beam irradiated C60 films.
Skone, Jonathan; Govoni, Marco; Galli, Giulia
Dielectric-dependent hybrid [DDH] functionals have recently been shown to yield highly accurate energy gaps and dielectric constants for a wide variety of solids, at a computational cost considerably less than standard GW calculations. The fraction of exact exchange included in the definition of DDH functionals depends (self-consistently) on the dielectric constant of the material. In the present talk we introduce a range-separated (RS) version of DDH functionals where short and long-range components are matched using material dependent, non-empirical parameters. Comparing with state of the art GW calculations and experiment, we show that such RS hybrids yield accurate electronic properties of both molecules and solids, including energy gaps, photoelectron spectra and absolute ionization potentials. This work was supported by NSF-CCI Grant Number NSF-CHE-0802907 and DOE-BES.
Electronic structures of N- and C-doped NiO from first-principles calculations
2010-01-01
The large intrinsic band gap of NiO has hindered severely its potential application under visible-light irradiation. In this study, we have performed first-principles calculations on the electronic properties of N- and C-doped NiO to ascertain if its band gap may be narrowed theoretically. It was found that impurity bands driven by N 2p or C 2p states appear in the band gap of NiO and that some of these locate at the conduction band minimum, which leads to a significant band gap narrowing. Ou...
Banerjee, Amartya S; Hu, Wei; Yang, Chao; Pask, John E
2016-01-01
The Discontinuous Galerkin (DG) electronic structure method employs an adaptive local basis set to solve the equations of density functional theory in a discontinuous Galerkin framework. The methodology is implemented in the Discontinuous Galerkin Density Functional Theory (DGDFT) code for large-scale parallel electronic structure calculations. In DGDFT, the basis is generated on-the-fly to capture the local material physics, and can systematically attain chemical accuracy with only a few tens of degrees of freedom per atom. Hence, DGDFT combines the key advantage of planewave basis sets in terms of systematic improvability with that of localized basis sets in reducing basis size. A central issue for large-scale calculations, however, is the computation of the electron density from the discretized Hamiltonian in an efficient and scalable manner. We show in this work how Chebyshev polynomial filtered subspace iteration (CheFSI) can be used to address this issue and push the envelope in large-scale materials si...
Electronic Structure and Elastic Properties of Ti3AlC from First-Principles Calculations
Institute of Scientific and Technical Information of China (English)
DU Yu-Lei
2009-01-01
We perform a first-principles study on the electronic structure and elastic properties of Ti3AlC with an antiper-ovskite structure. The absence of band gap at the Fermi level and the finite value of the density of states at the Fermi energy reveal the metallic behavior of this compound. The elastic constants of Ti_3AlC are derived yielding c_(11)=356 GPa, c_(12)= 55 GPa, c_(44)=157 GPa. The bulk modulus B, shear modulus G and Young's modulus E are determined to be 156, 151 and 342 GPa, respectively. These properties are compared with those of Ti_3AlC_2 and Ti_2AlC with a layered structure in the Ti-Al-C system and Fe_3AlC with the same antiperovskite structure.
Fan, S. W.; Song, T.; Huang, X. N.; Yang, L.; Ding, L. J.; Pan, L. Q.
2016-09-01
Utilizing the full potential linearized augment plane wave method, the electronic structures and magnetism for carbon doped CdSe are investigated. Calculations show carbon substituting selenium could induce CdSe to be a diluted magnetic semiconductor. Single carbon dopant could induce 2.00 μB magnetic moment. Electronic structures show the long-range ferromagnetic coupling mainly originates from the p-d exchange-like p-p coupling interaction. Positive chemical pair interactions indicate carbon dopants would form homogeneous distribution in CdSe host. The formation energy implies the non-equilibrium fabricated technology is necessary during the samples fabricated.
Canning, Andrew
2013-03-01
Inorganic scintillation phosphors (scintillators) are extensively employed as radiation detector materials in many fields of applied and fundamental research such as medical imaging, high energy physics, astrophysics, oil exploration and nuclear materials detection for homeland security and other applications. The ideal scintillator for gamma ray detection must have exceptional performance in terms of stopping power, luminosity, proportionality, speed, and cost. Recently, trivalent lanthanide dopants such as Ce and Eu have received greater attention for fast and bright scintillators as the optical 5d to 4f transition is relatively fast. However, crystal growth and production costs remain challenging for these new materials so there is still a need for new higher performing scintillators that meet the needs of the different application areas. First principles calculations can provide a useful insight into the chemical and electronic properties of such materials and hence can aid in the search for better new scintillators. In the past there has been little first-principles work done on scintillator materials in part because it means modeling f electrons in lanthanides as well as complex excited state and scattering processes. In this talk I will give an overview of the scintillation process and show how first-principles calculations can be applied to such systems to gain a better understanding of the physics involved. I will also present work on a high-throughput first principles approach to select new scintillator materials for fabrication as well as present more detailed calculations to study trapping process etc. that can limit their brightness. This work in collaboration with experimental groups has lead to the discovery of some new bright scintillators. Work supported by the U.S. Department of Homeland Security and carried out under U.S. Department of Energy Contract no. DE-AC02-05CH11231 at Lawrence Berkeley National Laboratory.
Institute of Scientific and Technical Information of China (English)
Guan Peng-Fei; Wang Chong-Yu; Yu Tao
2008-01-01
Local density functional is investigated by using the full-potential linearized augmented plane wave (FP-LAPW) method for ScN in the hexagonal structure and the rocksalt structure and for hexagonal structures linking a layered hexagonal phase with wurtzite structure along a homogeneous strain transition path. It is found that the wurtzite ScN is unstable and the layered hexagonal phase, labelled as ho, in which atoms are approximately fivefold coordinated,is metastable, and the rocksalt ScN is stable. The electronic structure, the physical properties of the intermediate structures and the energy band structure along the transition are presented. It is found that the band gaps change from 4.0 to 1.0eV continuously when c/a value varies from 1.68 to 1.26. It is noticeable that the study of ScN provides an opportunity to apply this kind of material (in wurtzite[h]-derived phase).
Energy Technology Data Exchange (ETDEWEB)
Song, T., E-mail: songting_lzjtu@yeah.net [School of Mathematics and Physics, Lanzhou Jiaotong University, Lanzhou 730070 (China); School of Material Science and Engineering, Lanzhou University of Technology, Lanzhou 730050 (China); Ma, Q. [School of Material Science and Engineering, Lanzhou University of Technology, Lanzhou 730050 (China); Sun, X.W., E-mail: xsun@carnegiescience.edu [School of Mathematics and Physics, Lanzhou Jiaotong University, Lanzhou 730070 (China); Geophysical Laboratory, Carnegie Institution of Washington, Washington, DC 20015 (United States); Liu, Z.J., E-mail: liuzj_lzcu@163.com [School of Mathematics and Physics, Lanzhou Jiaotong University, Lanzhou 730070 (China); Department of Physics, Lanzhou City University, Lanzhou 730070 (China); Fu, Z.J. [School of Electrical and Electronic Engineering, Chongqing University of Arts and Sciences, Chongqing 402160 (China); Wei, X.P.; Wang, T.; Tian, J.H. [School of Mathematics and Physics, Lanzhou Jiaotong University, Lanzhou 730070 (China)
2016-09-07
The phase transition, electronic band structure, and equation of state (EOS) of cubic TcN are investigated by first-principles pseudopotential method based on density-functional theory. The calculated enthalpies show that TcN has a transformation between zincblende and rocksalt phases and the pressure determined by the relative enthalpy is 32 GPa. The calculated band structure indicates the metallic feature and it might make cubic TcN a better candidate for hard materials. Particular attention is paid to the predictions of volume, bulk modulus and its pressure derivative which play a central role in the formulation of approximate EOSs using the quasi-harmonic Debye model. - Highlights: • The phase transition pressure and electronic band structure for cubic TcN are determined. • Particular attention is paid to investigate the equation of state parameters for cubic TcN. • The thermodynamic properties up to 80 GPa and 3000 K are successfully predicted.
Jónsson, Elvar Ö; Puska, Martti; Jónsson, Hannes
2016-01-01
An implementation of the generalized Pipek-Mezey method [Lehtola, S.; J\\'onsson, H. J. Chem. Theory Comput. 2014, 10, 642] for generating localized orbitals in periodic systems, i.e. Wannier functions, is described. The projector augmented wave (PAW) formalism for the representation of atomic core electrons is included in the implementation, which has been developed within the atomic simulation environment (ASE) software library. The implementation supports several different kinds of representations for the wave function, including real-space grids, plane waves or a linear combination of atomic orbitals. The implementation is tailored to the GPAW program but can easily be adapted to use output from various other electronic structure software packages such as ABINIT, NWChem, or VASP through interfaces in ASE. Generalized Pipek-Mezey Wannier functions (PMWF) are presented for both isolated molecules, as well as systems with periodicity in one, two and three dimensions. The method gives a set of highly localized...
Many-body electronic structure calculations of Eu-doped ZnO
Lorke, M.; Frauenheim, T.; da Rosa, A. L.
2016-03-01
The formation energies and electronic structure of europium-doped zinc oxide has been determined using DFT and many-body G W methods. In the absence of intrisic defects, we find that the europium-f states are located in the ZnO band gap with europium possessing a formal charge of 2+. On the other hand, the presence of intrinsic defects in ZnO allows intraband f -f transitions otherwise forbidden in atomic europium. This result corroborates with recently observed photoluminescence in the visible red region S. Geburt et al. [Nano Lett. 14, 4523 (2014), 10.1021/nl5015553].
Microscopic Calculation of the Inclusive Electron Scattering Structure Function in 16O
Mihaila, Bogdan; Heisenberg, Jochen H.
2000-02-01
We calculate the charge form factor and the longitudinal structure function for 16O and compare with the available experimental data, up to a momentum transfer of 4 fm-1. The ground-state correlations are generated using the coupled-cluster [ exp\\(S\\)] method, together with the realistic v18 NN interaction and the Urbana IX three-nucleon interaction. Center-of-mass corrections are dealt with by adding a center-of-mass Hamiltonian to the usual internal Hamiltonian, and by means of a many-body expansion for the computation of the observables measured in the center-of-mass system.
Microscopic calculation of the inclusive electron scattering structure function in O-16
Mihaila, B; Mihaila, Bogdan; Heisenberg, Jochen
2000-01-01
We calculate the charge form factor and the longitudinal structure function for $^{16}$O and compare with the available experimental data, up to a momentum transfer of 4 fm$^{-1}$. The ground state correlations are generated using the coupled cluster [exp(S}] method, together with the realistic v-18 NN interaction and the Urbana IX three-nucleon interaction. Center-of-mass corrections are dealt with by adding a center-of-mass Hamiltonian to the usual internal Hamiltonian, and by means of a many-body expansion for the computation of the observables measured in the center-of-mass system.
Ding, Li-Ping; Shao, Peng; Zhang, Fang-Hui; Lu, Cheng; Ding, Lei; Ning, Shu Ya; Huang, Xiao Fen
2016-07-18
On the basis of the first-principles techniques, we perform the structure prediction for MoB2. Accordingly, a new ground-state crystal structure WB2 (P63/mmc, 2 fu/cell) is uncovered. The experimental synthesized rhombohedral R3̅m and hexagonal AlB2, as well as theoretical predicted RuB2 structures, are no longer the most favorite structures. By analyzing the elastic constants, formation enthalpies, and phonon dispersion, we find that the WB2 phase is thermodynamically and mechanically stable. The high bulk modulus B, shear modulus G, low Poisson's ratio ν, and small B/G ratio are benefit to its low compressibility. When the pressure is 10 GPa, a phase transition is observed between the WB2-MoB2 and the rhombohedral R3̅m MoB2 phases. By analyzing the density of states and electron density, we find that the strong covalent is formed in MoB2 compounds, which contributes a great deal to its low compressibility. Furthermore, the low compressibility is also correlated with the local buckled structure.
Energy Technology Data Exchange (ETDEWEB)
Shi Hongliang [LCP, Institute of Applied Physics and Computational Mathematics, P.O. Box 8009, Beijing 100088 (China)] [State Key Laboratory for Superlattices and Microstructures, Institute of Semiconductors, Chinese Academy of Sciences, P.O. Box 912, Beijing 100083 (China); Zhang Ping, E-mail: zhang_ping@iapcm.ac.c [LCP, Institute of Applied Physics and Computational Mathematics, P.O. Box 8009, Beijing 100088 (China)] [Center for Applied Physics and Technology, Peking University, Beijing 100871 (China); Li Shushen [State Key Laboratory for Superlattices and Microstructures, Institute of Semiconductors, Chinese Academy of Sciences, P.O. Box 912, Beijing 100083 (China); Sun Bo [LCP, Institute of Applied Physics and Computational Mathematics, P.O. Box 8009, Beijing 100088 (China); Wang Baotian [Institute of Theoretical Physics and Department of Physics, Shanxi University, Taiyuan 030006 (China)
2009-09-21
The electronic structure, elastic constants, Poisson's ratio, and phonon dispersion curves of UC have been systematically investigated from the first-principles calculations by the projector-augmented-wave (PAW) method. In order to describe precisely the strong on-site Coulomb repulsion among the localized U 5f electrons, we adopt the local density approximation (LDA)+U and generalized gradient approximation (GGA)+U formalisms for the exchange correlation term. We systematically study how the electronic properties and elastic constants of UC are affected by the different choice of U as well as the exchange-correlation potential. We show that by choosing an appropriate Hubbard U parameter within the GGA+U approach, most of our calculated results are in good agreement with the experimental data. Therefore, the results obtained by the GGA+U with effective Hubbard parameter U chosen around 3 eV for UC are considered to be reasonable.
Energy Technology Data Exchange (ETDEWEB)
Climent, Clàudia [Departament de Química Física, Institut de Química Teòrica i Computacional (IQTCUB), Universitat de Barcelona, Martí i Franquès, 1-11, 08028 Barcelona (Spain); Casanova, David, E-mail: david.casanova@ehu.es [IKERBASQUE, Basque Foundation for Science, 48011 Bilbao, Euskadi, Spain, and Kimika Fakultea, Euskal Herriko Unibertsitatea (UPV/EHU), Donostia, Euskadi, Spain. (Spain)
2013-09-23
Highlights: • We study D-π-A dyes with polythiophene (Tn) or polycyclopentadithiophene (Cn) linkers. • Molecular geometry plays a crucial role in the photophysical properties of organic dyes. • Cn linkers induce lower transition energies and larger oscillator strengths than Tn separators. • We discuss a variety of computational tools to quantify the CT nature of electronic transitions. • We compute ground and excited state oxidation potentials with a long-range corrected functional. - Abstract: In this work we present a detailed study of the atomic and electronic structure of a collection of push–pull organic dyes for high-performance sensitized solar cells (DSSCs). We compare the computed photophysical properties of donor-bridge-acceptor (D-π-A) dyes with polythiophene (Tn) or polycyclopentadithiophene (Cn) conjugated linkers with up to four fused thiophene rings. Excitation energies to lowest excited singlet state have been rationalized by means of fragment and molecular orbitals. Vertical and adiabatic excitation energies are systematically lower for the Cn family and become smaller with the length of the molecular conjugation. We discuss a large variety of computational techniques for the characterization of the charge transfer (CT) nature of the electronic excitation. In addition to standard procedures to quantify CT character, we propose and explain several novel interaction based measures of CT. Finally, we have computed ground and excited state oxidation potentials (GSOP and ESOP) with long-range corrected (LRC) functional.
Electronic structure of RScO{sub 3} from x-ray spectroscopies and first-principles calculations
Energy Technology Data Exchange (ETDEWEB)
Derks, Christine; Neumann, Manfred [Department of Physics, University of Osnabrueck (Germany); Kuepper, Karsten [Department of Solid State Physics, University of Ulm (Germany); Postnikov, Andree [Laboratoire de Physique des Milieux Denses, Universite Paul Verlaine, Metz (France); Uecker, Reinhard [Institute for Crystal Growth, Berlin (Germany)
2011-07-01
Perovskites of the type RScO{sub 3}, where R represents a trivalent rare-earth metal, are high k materials and belong to the best available thin film substrates for the epitaxial growth of high quality thin films. This allows a so called strain tailoring of ferroelectric, ferromagnetic, or multiferroic perovskite thin films by choosing different RScO{sub 3}. With respect to these interesting properties there is up to now only rare knowledge available about the electronic structure of RScO{sub 3}. In a previous work we have already published a work on the electronic structure of SmScO{sub 3}, GdScO{sub 3}, and DyScO{sub 3}. As far as we know, it is the only work combining XPS, XES and XAS with ab initio electronic structure calculations. We are extending these successful investigations to single crystalline PrScO{sub 3}, NdScO{sub 3}, EuScO{sub 3} and TbScO{sub 3}. A complete electronic structure was obtained and the band gaps could be deduced for all these rare-earth scandates. All the results were found to be in good agreement with LDA+U calculations.
Institute of Scientific and Technical Information of China (English)
WEN QingBo; YU ShanSheng; ZHENG WeiTao
2009-01-01
Calculations have been made for single-walled zigzag (n, 0) carbon nanotubes containing substitutional boron impurity atoms using ab initio density functional theory. It is found that the formation energies of these nanotubes depend on the tube diameter, as do the electronic properties, and show periodic fea-ture that results from their different π bonding structures compared to those of perfect zigzag carbon nanotubes. When more boron atoms are incorporated into a single-walled zigzag carbon nanotube, the substitutional boron atoms tend to come together to form structure of BC3 nanodomains, and B-doped tubes have striking acceptor states above the top of the valence bands. For the structure of BC3, there are two kinds of configurations with different electronic structures.
Institute of Scientific and Technical Information of China (English)
无
2009-01-01
Calculations have been made for single-walled zigzag(n,0) carbon nanotubes containing substitutional boron impurity atoms using ab initio density functional theory.It is found that the formation energies of these nanotubes depend on the tube diameter,as do the electronic properties,and show periodic fea-ture that results from their different π bonding structures compared to those of perfect zigzag carbon nanotubes.When more boron atoms are incorporated into a single-walled zigzag carbon nanotube,the substitutional boron atoms tend to come together to form structure of BC3 nanodomains,and B-doped tubes have striking acceptor states above the top of the valence bands.For the structure of BC3,there are two kinds of configurations with different electronic structures.
Galvan, D H
2003-01-01
To get insight into the electronic properties of PrFe4P12 skutterudite, band electronic structure calculations, Total and Projected Density of States, Crystal Orbital Overlap Population and Mulliken Population Analysis were performed. The energy bands yield a semi metallic behavior with a direct gap (at gamma) of 0.02 eV. Total and Projected Density of States provided information of the contribution from each orbital of each atom to the total Density of States. Moreover, the bonding strength between some atoms within the unit cell was obtained. Mulliken Population analysis suggests ionic behavior for this compound.
Ma, Chao; Yang, Huaixin; Tian, Huanfang; Shi, Honglong; Wang, Zhiwei; Li, Jianqi
2013-03-20
Using electron energy loss spectroscopy (EELS) measurements and first-principles electronic structure calculations, the significant interlayer hybridization between the insulating layers (ReO or Ba) and the conducting FeAs layers was investigated in the layered iron pnictides, which is quite different from the case in the cuprate superconductors. This interlayer hybridization would result in an increase in the bandwidth near the Fermi level and interorbital charge transfer in the Fe 3d orbitals, which subsequently leads to a decrease in the Fe local moment and the modification of the Fermi surface topology. Therefore, a three-dimensional character of the electronic structure due to the interlayer hybridization is expected, as observed in previous experiments. These findings indicate that reduced dimensionality is no longer a necessary condition in the search for high-T(c) superconductors in iron pnictides.
Close-coupling calculations of fine-structure excitation of Ne II due to H and electron collisions
Stancil, Phillip C.; Cumbee, Renata; Wang, Qianxia; Loch, Stuart; Pindzola, Michael; Schultz, David R.; Buenker, Robert; McLaughlin, Brendan; Ballance, Connor
2016-06-01
Fine-structure transitions within the ground term of ions and neutral atoms dominate the cooling in a variety of molecular regions and also provide important density and temperature diagnostics. While fine-structure rates due to electron collisions have been studied for many systems, data are generally sparse for elements larger than oxygen, at low temperatures, and for collisions due to heavy particles. We provide rate coefficients for H collisions for the first time. The calculations were performed using the quantum molecular-orbital close-coupling approach and the elastic approximation. The heavy-particle collisions use new potential energies for the lowest-lying NeH+ states computed with the MRDCI method. The focus of the electron-impact calculations is to provide fine-structure excitation rate coefficients down to 10 K. We compare with previous calculations at higher temperatures (Griffin et al. 2001), and use a range of calculations to provide an estimate of the uncertainty on our recommended rate coefficients. A brief discussion of astrophysical applications is also provided.Griffin, D.C., et al., 2001, J. Phys. B, 34, 4401This work partially supported by NASA grant No. NNX15AE47G.
Institute of Scientific and Technical Information of China (English)
LU Lai-Yu; WEI Dong-Qing; CHEN Xiang-Rong; JI Guang-Fu
2008-01-01
Structures and electronic properties of the pentaerythritol (PE) crystal under volume compression up to 0.85Vo are studied by E - V fitting method using density functional theory (DFT). The compression dependences of the cell volumes, lattice constants, and molecular geometries of solid PE are presented and discussed. It is found that the solid PE presents anisotropy along a- and c-axes, and the c axis is the most compressible. Decreasing anisotropy ratio (c/a) with elevating compression suggests an enhancement of the vdW interaction with increasing compression. The C-C and C-H bonds are significantly reduced under compression, which may be related to the sensitivity. The solid PE has indirect band gap (X - C) in the range of the researched compression and the band gap is decreased with compression.
GPAW - massively parallel electronic structure calculations with Python-based software
DEFF Research Database (Denmark)
Enkovaara, Jussi; Romero, Nichols A.; Shende, Sameer
2011-01-01
popular choice. While dynamic, interpreted languages, such as Python, can increase the effciency of programmer, they cannot compete directly with the raw performance of compiled languages. However, by using an interpreted language together with a compiled language, it is possible to have most...... of the productivity enhancing features together with a good numerical performance. We have used this approach in implementing an electronic structure simulation software GPAW using the combination of Python and C programming languages. While the chosen approach works well in standard workstations and Unix...... environments, massively parallel supercomputing systems can present some challenges in porting, debugging and profiling the software. In this paper we describe some details of the implementation and discuss the advantages and challenges of the combined Python/C approach. We show that despite the challenges...
Labra-Vázquez, Pablo; Palma-Contreras, Miguel; Santillan, Rosa; Farfán, Norberto
2017-03-01
The molecular structure of 1-[2-oxo-2-(2-pyridinyl)ethyl]pyridinium iodide (C12H11IN2O) is discussed using an experimental (FT-IR/ATR, NMR, SXRD) and theoretical (DFT, B3LYP/6-311G**) approach. Compound 2 crystallized in the monoclinic P21/c space group with 4 molecules per unit cell and unit cell dimensions a = 7.5629 Å (3), b = 21.5694 Å (7), c = 7.8166 Å (3). The crystal packing is governed by ion-dipole contacts and π-π stacking. High electrostatic potential at the ethanone hydrogens was derived from DFT calculations, further explaining the acidity and reactivity of the molecule as a Michael donor.
Kong, Bo; Zhang, Yachao
2016-07-01
The electronic structures of the cubic GdH3 are extensively investigated using the ab initio many-body GW calculations treating the Gd 4f electrons either in the core (4f-core) or in the valence states (4f-val). Different degrees of quasiparticle (QP) self-consistent calculations with the different starting points are used to correct the failures of the GGA/GGA + U/HSE03 calculations. In the 4f-core case, GGA + G0W0 calculations give a fundamental band gap of 1.72 eV, while GGA+ GW0 or GGA + GW calculations present a larger band gap. In the 4f-val case, the nonlocal exchange-correlation (xc) functional HSE03 can account much better for the strong localization of the 4f states than the semilocal or Hubbard U corrected xc functional in the Kohn-Sham equation. We show that the fundamental gap of the antiferromagnetic (AFM) or ferromagnetic (FM) GdH3 can be opened up by solving the QP equation with improved starting point of eigenvalues and wave functions given by HSE03. The HSE03 + G0W0 calculations present a fundamental band gap of 2.73 eV in the AFM configuration, and the results of the corresponding GW0 and GW calculations are 2.89 and 3.03 eV, respectively. In general, for the cubic structure, the fundamental gap from G0W0 calculations in the 4f-core case is the closest to the real result. By G0W0 calculations in the 4f-core case, we find that H or Gd defects can strongly affect the band structure, especially the H defects. We explain the mechanism in terms of the possible electron correlation on the hydrogen site. Under compression, the insulator-to-metal transition in the cubic GdH3 occurs around 40 GPa, which might be a satisfied prediction.
Valence electron structure of the（ZrTi）B2 solid solutions calculated by the three models
Institute of Scientific and Technical Information of China (English)
无
2009-01-01
The Zr-rich(Zr0.8Ti0.2)B2 and the Ti-rich(Ti0.8Zr0.2)B2 solid solutions are formed when TiB2 and ZrB2 are hot-pressed.To forecast the properties of the two solid solutions,their valence electron structure was analyzed based on the empirical electron theory(EET) of solids and molecules.We used three different models,the average atom model,the average cell model and the real cell model,and compared with the calculation results from the three models.In the real cell model,the lattice constants of the solid solu-tions were supposed to be changed or unchanged.The results showed that different models could only result in slight change in the hybridization levels of the metal atoms in the two solid solutions and little difference between the calculation values.However,they can not change the variant trend of the va-lence electron structure nor the properties of the solid solutions.Thus,the three models and the methods are appropriate and the calculation results are reasonable and consistent.
Valence electron structure of the (ZrTi)B2 solid solutions calculated by the three models
Institute of Scientific and Technical Information of China (English)
LI JinPing; HAN JieCai; MENG SongHe; WANG BaoLin
2009-01-01
The Zr-rich (Zr0.8Ti0.2)B2 and the Ti-rich Zr0.8Ti0.2)B2 solid solutions are formed when TiB2 and ZrB2 are hot-pressed. To forecast the properties of the two solid solutions, their valence electron structure was analyzed based on the empirical electron theory (EET) of solids and molecules. We used three differen tmodels, the average atom model, the average cell model and the real cell model, and compared with the calculation results from the three models. In the real cell model, the lattice constants of the solid solu-tions were supposed to be changed or unchanged. The results showed that different models could only result in slight change in the hybridization levels of the metal atoms in the two solid solutions and little difference between the calculation values. However, they can not change the variant trend of the va-lence electron structure nor the properties of the solid solutions. Thus, the three models and the methods are appropriate and the calculation results are reasonable and consistent.
Institute of Scientific and Technical Information of China (English)
Yun Jiang-Ni; Zhang Zhi-Yong
2009-01-01
This paper investigates the effect of Nb doping on the electronic structure and optical properties of by the first-principles calculation of plane wave ultra-soft pseudo-potential based on density functional theory (DFT).The calculated results reveal that due to the electron doping, the Fermi level shifts into conduction bands(CBs) for Sr2NbxTi1-xO4 with x = 0.125 and the system shows n-type degenerate semiconductor features. Sr2TiO4 exhibits optical anisotropy in its main crystal axes, and the c-axis shows the most suitable crystal growth direction for obtaining a wide transparent region. The optical transmittance is higher than 90% in the visible range for Sr2Nb0.125Ti0.875O4.
Electronic band structure and specific features of Sm{sub 2}NiMnO{sub 6} compound: DFT calculation
Energy Technology Data Exchange (ETDEWEB)
Reshak, A.H. [Institute of complex systems, FFPW, CENAKVA, University of South Bohemia in CB, Nove Hrady 37333 (Czech Republic); Center of Excellence Geopolymer and Green Technology, School of Material Engineering, University Malaysia Perlis, 01007 Kangar, Perlis (Malaysia); Azam, Sikander, E-mail: sikander.physicst@gmail.com [Institute of complex systems, FFPW, CENAKVA, University of South Bohemia in CB, Nove Hrady 37333 (Czech Republic)
2013-09-15
The band structure, density of states, electronic charge density, Fermi surface and optical properties of Sm{sub 2}NiMnO{sub 6} compound have been investigated with the support of density functional theory (DFT). The atomic positions of Sm{sub 2}NiMnO{sub 6} compound were optimized by minimizing the forces acting on the atoms, using the full potential linear augmented plane wave method. We employed the local density approximation (LDA), generalized gradient approximation (GGA) and Engel–Vosko GGA (EVGGA) to treat the exchange correlation potential by solving Kohn–Sham equations. The calculation shows that the compound is metallic with strong hybridization near the Fermi energy level (E{sub F}). The calculated density of states at the E{sub F} is about 21.60, 24.52 and 26.21 states/eV, and the bare linear low-temperature electronic specific heat coefficient (γ) is found to be 3.74, 4.25 and 4.54 mJ/mol K{sup 2} for EVGGA, GGA and LDA, respectively. The Fermi surface is composed of two sheets. The bonding features of the compounds are analyzed using the electronic charge density in the (011) crystallographic plane. The dispersion of the optical constants was calculated and discussed. - Highlights: • The compound is metallic with strong hybridization near the Fermi energy. • The density of states at the Fermi energy is calculated. • The bare linear low-temperature electronic specific heat coefficient is obtained. • Fermi surface is composed of two sheets. • The bonding features are analyzed using the electronic charge density.
Wang, Ya-Ting; Gao, Yuan-Jun; Wang, Qian; Cui, Ganglong
2017-02-02
Intramolecularly bridged diarylethenes exhibit improved photocyclization quantum yields because the anti-syn isomerization that originally suppresses photocyclization in classical diarylethenes is blocked. Experimentally, three possible channels have been proposed to interpret experimental observation, but many details of photochromic mechanism remain ambiguous. In this work we have employed a series of electronic structure methods (OM2/MRCI, DFT, TDDFT, RI-CC2, DFT/MRCI, and CASPT2) to comprehensively study excited state properties, photocyclization, and photoreversion dynamics of 1,2-dicyano[2,2]metacyclophan-1-ene. On the basis of optimized stationary points and minimum-energy conical intersections, we have refined experimentally proposed photochromic mechanism. Only an S1/S0 minimum-energy conical intersection is located; thus, we can exclude the third channel experimentally proposed. In addition, we find that both photocyclization and photoreversion processes use the same S1/S0 conical intersection to decay the S1 system to the S0 state, so we can unify the remaining two channels into one. These new insights are verified by our OM2/MRCI nonadiabatic dynamics simulations. The S1 excited-state lifetimes of photocyclization and photoreversion are estimated to be 349 and 453 fs, respectively, which are close to experimentally measured values: 240 ± 60 and 250 fs in acetonitrile solution. The present study not only interprets experimental observations and refines previously proposed mechanism but also provides new physical insights that are valuable for future experiments.
Electronic structure of ScN and YN:density-functional theory LDA and GW approximation calculations
Institute of Scientific and Technical Information of China (English)
Lü Tie-Yu; Huang Mei-Chun
2007-01-01
The desirable physical properties of hardness, high temperature stability, and conductivity make the early transition metal nitrides important materials for various technological applications. To learn more about the nature of these materials, the local-density approximation(LDA) and GW approximation i.e. combination of the Green function G and the screened Coulomb interaction W, have been performed. This paper investigates the bulk electronic and physical properties of early transition metal mononitrides, ScN and YN in the rocksalt structure. In this paper, the semicore electrons are regarded as valance electrons. ScN appears to be a semimetal, and YN is semiconductor with band gap of0.142 eV within the LDA, but are in fact semiconductors with indirect band gaps of 1.244 and 0.544 eV respectively, as revealed by calculations performed using GW approximation.
Baldea, Ioan
2012-01-01
In cases where reorganization is important, present theoretical studies of molecular transport have inherently to resort to models. The Newns-Anderson model is ubiquitous for this purpose but, to author's knowledge, attempts to validate/challenge this model by microscopic calculations are missing in the literature. In this work, results of electronic structure calculations are presented, which demonstrate that the conventional Newns-Anderson model fails to describe redox-active tunneling junctions of recent experimental interest. For the case considered, the ($4, 4^\\prime$)-bipyridine molecule, the failure traces back to the floppy degree of freedom represented by the relative rotation of the two pyridine rings. Expressions that generalize the Newns-Anderson model are deduced, which include significant anharmonicities. These expressions can be straightforwardly utilized as input information in calculations of the partially coherent transport.
Electronic structure of RScO{sub 3} from x-ray spectroscopies and first-principles calculations
Energy Technology Data Exchange (ETDEWEB)
Derks, Christine; Raekers, Michael; Neumann, Manfred [Department of Physics, University of Osnabrueck, D-49069 Osnabrueck (Germany); Kuepper, Karsten [Departement of Solidstate Physics, Univeristy of Ulm, D-89069 Ulm (Germany); Postnikov, Andree [Laboratoire de Physique des Milieux Denses, Universite Paul Verlaine, Metz (France); Uecker, Reinhard [Institute for Crystal Growth, D-12489 Berlin (Germany)
2010-07-01
Perovskites of the type RScO{sub 3}, where R represents a trivalent rare-earth metal, exhibit an enormous variety of physical properties and can be used for different applications. They are high k materials and belong to the best available thin film substrates for the epitaxial growth of high quality thin films. This allows a so called strain tailoring of ferroelectric, ferromagnetic, or multiferroic perovskite thin films by choosing different RScO{sub 3}. The electronic structures of a series of RScO{sub 3} single crystals are investigated by means of x-ray photoelectron spectroscopy (XPS), X-ray emission spectroscopy (XES), X-ray absorption spectroscopy (XAS) and band structure calculations. By combining XES and XAS measurements together with theoretical calculations the band gaps of the compounds can be accurately determined. The presented results will broaden the complete experimental and theoretical picture of the valence bands of RScO{sub 3} series.
Energy Technology Data Exchange (ETDEWEB)
Sesion Jr, P D [Escola de Ciencias e Tecnologia, Universidade Federal do Rio Grande do Norte, 59072-970 Natal, Rio Grande do Norte (Brazil); Henriques, J M [Departamento de Fisica Teorica e Experimental, Universidade Federal do Rio Grande do Norte, 59072-970 Natal, Rio Grande do Norte (Brazil); Barboza, C A; Albuquerque, E L [Departamento de Biofisica e Farmacologia, Universidade Federal do Rio Grande do Norte, 59072-900 Natal, Rio Grande do Norte (Brazil); Freire, V N [Departamento de Fisica, Universidade Federal do Ceara, 60455-970 Fortaleza, Ceara (Brazil); Caetano, E W S, E-mail: ewcaetano@gmail.co [Instituto Federal de Educacao, Ciencia e Tecnologia do Ceara, Avenida 13 de Maio, 2081, Benfica, 60040-531 Fortaleza, Ceara (Brazil)
2010-11-03
CdSnO{sub 3} ilmenite and perovskite crystals were investigated using both the local density and generalized gradient approximations, LDA and GGA, respectively, of the density functional theory (DFT). The electronic band structures, densities of states, dielectric functions, optical absorption and reflectivity spectra related to electronic transitions were obtained, as well as the infrared absorption spectra after computing the vibrational modes of the crystals at q = 0. Dielectric optical permittivities and polarizabilities at {omega} = 0 and {infinity} were also calculated. The results show that GGA-optimized geometries are more accurate than LDA ones, and the Kohn-Sham band structures obtained for the CdSnO{sub 3} polymorphs confirm that ilmenite has an indirect band gap, while perovskite has a direct band gap, both being semiconductors. Effective masses for both crystals are obtained for the first time, being highly isotropic for electrons and anisotropic for holes. The optical properties reveal a very small degree of anisotropy of both crystals with respect to different polarization planes of incident light. The phonon calculation at q = 0 for perovskite CdSnO{sub 3} does not show any imaginary frequencies, in contrast to a previous report suggesting the existence of a more stable crystal of perovskite CdSnO{sub 3} with ferroelectric properties.
Sesion, P D; Henriques, J M; Barboza, C A; Albuquerque, E L; Freire, V N; Caetano, E W S
2010-11-03
CdSnO(3) ilmenite and perovskite crystals were investigated using both the local density and generalized gradient approximations, LDA and GGA, respectively, of the density functional theory (DFT). The electronic band structures, densities of states, dielectric functions, optical absorption and reflectivity spectra related to electronic transitions were obtained, as well as the infrared absorption spectra after computing the vibrational modes of the crystals at q = 0. Dielectric optical permittivities and polarizabilities at ω = 0 and ∞ were also calculated. The results show that GGA-optimized geometries are more accurate than LDA ones, and the Kohn-Sham band structures obtained for the CdSnO(3) polymorphs confirm that ilmenite has an indirect band gap, while perovskite has a direct band gap, both being semiconductors. Effective masses for both crystals are obtained for the first time, being highly isotropic for electrons and anisotropic for holes. The optical properties reveal a very small degree of anisotropy of both crystals with respect to different polarization planes of incident light. The phonon calculation at q = 0 for perovskite CdSnO(3) does not show any imaginary frequencies, in contrast to a previous report suggesting the existence of a more stable crystal of perovskite CdSnO(3) with ferroelectric properties.
Kleisath, Elizabeth; Marta, Rick A; Martens, Sabrina; Martens, Jon; McMahon, Terry
2015-06-25
Gas-phase clusters of protonated methylamine and phenylalanine (Phe) derivatives have been studied using infrared multiple photon dissociation (IRMPD) spectroscopy in combination with electronic structure calculations at the MP2/aug-cc-pVTZ//B3LYP/6-311+G(d,p) level of theory. Experiments were performed on several Phe derivatives including 4-chloro-l-phenylalanine (4Chloro-Phe), 4-nitro-l-phenylalanine (4Nitro-Phe), 3-cyano-l-phenylalanine (3Cyano-Phe), and 3-trifluoromethyl-l-phenylalanine (3CF3-Phe). Through comparisons between experimental IRMPD spectra and stimulated spectra obtained by electronic structure calculations, charge-solvated structures were found to be prevalent in both 4Chloro-Phe and 4Nitro-Phe, whereas 3Cyano-Phe favored zwitterionic structures and 3-CF3-Phe likely have both zwitterionic and charge-solvated structures present.
Institute of Scientific and Technical Information of China (English)
ZHANG Zhi-jie; LIU Yu-hua; L(U) Zhong-yuan; LI Ze-sheng
2009-01-01
The rotational isomeric state(RIS) model was constructed for poly(vinylidene chloride)(PVDC) based on quantum chemistry calculations. The statistical weighted parameters were obtained from RIS representations and ab initio energies of conformers for model molecules 2,2,4,4-tetrachloropentane(TCP) and 2,2,4,4,6, 6-hexachlorohep-tane(HCH). By employing the RIS method, the characteristic ratio C∞ was calculated for PVDC. The calculated cha-racteristic ratio for PVDC is in good agreement with experiment result. Additionally, we studied the influence of the statistical weighted parameters on C∞ by calculating δC∞/δlnw. According to the values of δC∞/δlnw, the effects of second-order Cl-CH2 pentane type interaction and Cl-Cl long range interaction on C∞ were found to be important. In contrast, first-order interaction is unimportant.
First-Principles Band Calculations on Electronic Structures of Ag-Doped Rutile and Anatase TiO2
Institute of Scientific and Technical Information of China (English)
HOU Xing-Gang; LIU An-Dong; HUANG Mei-Dong; LIAO Bin; WU Xiao-Ling
2009-01-01
The electronic structures of Ag-doped rutile and anatase TiO2 are studied by first-principles band calculations based on density funetionai theory with the full-potentiai linearized-augraented-plane-wave method.New occupied bands ore found between the band gaps of both Ag-doped rutile and anatase TiO2.The formation of these new bands Capri be explained mainly by their orbitals of Ag 4d states mixed with Ti 3d states and are supposed to contribute to their visible light absorption.
Hamioud, L.; Boumaza, A.; Touam, S.; Meradji, H.; Ghemid, S.; El Haj Hassan, F.; Khenata, R.; Omran, S. Bin
2016-06-01
The present paper aims to study the structural, electronic, optical and thermal properties of the boron nitride (BN) and BAs bulk materials as well as the BNxAs1-x ternary alloys by employing the full-potential-linearised augmented plane wave method within the density functional theory. The structural properties are determined using the Wu-Cohen generalised gradient approximation that is based on the optimisation of the total energy. For band structure calculations, both the Wu-Cohen generalised gradient approximation and the modified Becke-Johnson of the exchange-correlation energy and potential, respectively, are used. We investigated the effect of composition on the lattice constants, bulk modulus and band gap. Deviations of the lattice constants and the bulk modulus from the Vegard's law and the linear concentration dependence, respectively, were observed for the alloys where this result allows us to explain some specific behaviours in the electronic properties of the alloys. For the optical properties, the calculated refractive indices and the optical dielectric constants were found to vary nonlinearly with the N composition. Finally, the thermal effect on some of the macroscopic properties was predicted using the quasi-harmonic Debye model in which the lattice vibrations are taken into account.
Korotin, M. A.; Pchelkina, Z. V.; Skorikov, N. A.; Efremov, A. V.; Anisimov, V. I.
2016-07-01
Based on the coherent potential approximation, the method of calculating the electronic structure of nonstoichiometric and hyperstoichiometric compounds with strong electron correlations and spin-orbit coupling has been developed. This method can be used to study both substitutional and interstitial impurities, which is demonstrated based on the example of the hyperstoichiometric UO2.12 compound. The influence of the coherent potential on the electronic structure of compounds has been shown for the nonstoichiometric UO1.87 containing vacancies in the oxygen sublattice as substitutional impurities, for stoichiometric UO2 containing vacancies in the oxygen sublattice and oxygen as an interstitial impurity, and for hyperstoichiometric UO2.12 with excess oxygen also as interstitial impurity. In the model of the uniform distribution of impurities, which forms the basis of the coherent potential approximation, the energy spectrum of UO2.12 has a metal-like character.
Pimenov, Oleg A.; Belova, Natalya V.; Sliznev, Valery V.
2017-03-01
The molecular structure of tris-2,2,6,6-tetramethyl-heptane-3,5-dione thulium, or Tm(thd)3, has been studied by gas-phase electron diffraction monitored by mass spectrometry (GED/MS) and quantum chemical (DFT) calculations. Both the DFT(PBE0) calculations and the GED data collected at 400(8) K indicate that the molecules have D3 symmetry with a distorted antiprismatic TmO6 coordination geometry. According to GED refinements the twist angle θ, i.e. the angle of rotation of the upper O3 triangles relative to their position in regular prism is θ = 16.9(2.0)0. This value is close to both the equilibrium value obtained from the DFT calculations and to the thermal average value at the temperature of the GED experiment obtained by integration over the DFT potential energy surface. The bond distances (rh1) in the chelate ring are Tmsbnd O = 2.214(5) Å, Csbnd O = 1.278(4) Å, and Csbnd C = 1.404(3) Å. The DFT calculations yielded structure parameters in close agreement with those found experimentally. As an alternative to conventional Lewis model which was realized in NBO the topological analysis of ρ(r) in the frame of Bader's quantum theory of atoms in molecule (QTAIM) was performed.
Curie temperatures of dilute magnetic semiconductors from LDA+U electronic structure calculations
Energy Technology Data Exchange (ETDEWEB)
Sato, K. [ISIR, Osaka University, 8-1 Mihogaoka, Ibaraki, Osaka 567-0047 (Japan)]. E-mail: ksato@cmp.sanken.osaka-u.ac.jp; Dederichs, P.H. [IFF, Forschungszentrum Juelich, D-52425 Juelich (Germany); Katayama-Yoshida, H. [ISIR, Osaka University, 8-1 Mihogaoka, Ibaraki, Osaka 567-0047 (Japan)
2006-04-01
The magnetic properties of dilute magnetic semiconductors (DMS) are calculated by using the local density approximation +U(LDA+U) method. In the LDA+U, occupied d-states in (Ga, Mn)As are predicted at lower energy than in the LDA and p-d exchange interaction explains calculated concentration dependence of Curie temperature very well. In (Ga, Mn)N, unoccupied d states are predicted at higher energy by LDA+U, resulting in higher Curie temperatures than in LDA at high concentrations due to the suppression of the anti-ferromagnetic super-exchange interaction.
A Detailed Derivation of Gaussian Orbital-Based Matrix Elements in Electron Structure Calculations
Petersson, T.; Hellsing, B.
2010-01-01
A detailed derivation of analytic solutions is presented for overlap, kinetic, nuclear attraction and electron repulsion integrals involving Cartesian Gaussian-type orbitals. It is demonstrated how s-type orbitals can be used to evaluate integrals with higher angular momentum via the properties of Hermite polynomials and differentiation with…
Is C-50 a superaromat? Evidence from electronic structure and ring current calculations
Matias, Ana Sanz; Havenith, Remco W. A.; Alcami, Manuel; Ceulemans, Arnout
2016-01-01
The fullerene-50 is a 'magic number' cage according to the 2(N + 1)(2) rule. For the three lowest isomers of C-50 with trigonal and pentagonal symmetries, we calculate the sphericity index, the spherical parentage of the occupied p-orbitals, and the current density in an applied magnetic field. The
Energy Technology Data Exchange (ETDEWEB)
Tucker, Jon R.; Magyar, Rudolph J.
2012-02-01
High explosives are an important class of energetic materials used in many weapons applications. Even with modern computers, the simulation of the dynamic chemical reactions and energy release is exceedingly challenging. While the scale of the detonation process may be macroscopic, the dynamic bond breaking responsible for the explosive release of energy is fundamentally quantum mechanical. Thus, any method that does not adequately describe bonding is destined to lack predictive capability on some level. Performing quantum mechanics calculations on systems with more than dozens of atoms is a gargantuan task, and severe approximation schemes must be employed in practical calculations. We have developed and tested a divide and conquer (DnC) scheme to obtain total energies, forces, and harmonic frequencies within semi-empirical quantum mechanics. The method is intended as an approximate but faster solution to the full problem and is possible due to the sparsity of the density matrix in many applications. The resulting total energy calculation scales linearly as the number of subsystems, and the method provides a path-forward to quantum mechanical simulations of millions of atoms.
Buchalski, Piotr; Kamińska, Elzbieta; Piwowar, Katarzyna; Suwińska, Kinga; Jerzykiewicz, Lucjan; Rossi, Fulvio; Laschi, Franco; de Biani, Fabrizia Fabrizi; Zanello, Piero
2009-06-01
Reactions of 9-nickelafluorenyllithium with cobalt and nickel pentamethylcyclopentadienyl-acetylacetonates resulted in the formation of the novel nickelacyclic-cobaltocene 2 and nickelacyclic-nickelocene 3, respectively, in which the central metal atom is bonded to the nickelafluorenyl ring. On the basis of their redox propensity, compounds 2 and 3 were oxidized to the corresponding monocations [2](+) and [3](+). The crystal and molecular structures of both the redox couples were determined by single-crystal X-ray analysis. In spite of their structural similarity, they display a rather different electron transfer ability. To throw light on such an aspect, the pertinent redox couples have been examined by EPR spectroscopy and the nature of the frontier orbitals involved in the redox activity of the neutral precursors has been supported by extended Huckel theoretical calculations.
García-Risueño, Pablo; Oliveira, Micael J T; Andrade, Xavier; Pippig, Michael; Muguerza, Javier; Arruabarrena, Agustin; Rubio, Angel
2012-01-01
We present an analysis of different methods to calculate the classical electrostatic Hartree potential created by charge distributions. Our goal is to provide the reader with an estimation on the performance ---in terms of both numerical complexity and accuracy--- of popular Poisson solvers, and to give an intuitive idea on the way these solvers operate. Highly parallelisable routines have been implemented in the first-principle simulation code Octopus to be used in our tests, so that reliable conclusions about the capability of methods to tackle large systems in cluster computing can be obtained from our work.
DEFF Research Database (Denmark)
Vanin, Marco; Gath, Jesper; Thygesen, Kristian Sommer;
2010-01-01
The stability of graphene nanoribbons in the presence of typical atmospheric molecules is systematically investigated by means of density-functional theory. We calculate the edge formation free energy of five different edge configurations passivated by H, H-2, O, O-2, N-2, CO, CO2, and H2O......, respectively. In addition to the well known hydrogen passivated armchair and zigzag edges, we find the edges saturated by oxygen atoms to be particularly stable under atmospheric conditions. Saturation of the zigzag edge by oxygen leads to the formation of metallic states strictly localized on the oxygen atoms...
Institute of Scientific and Technical Information of China (English)
Zeng Hui; Zhao Jun; Xiao Xun
2013-01-01
Quantum chemical calculations are performed to investigate the equilibrium C-COOH bond distances and the bond dissociation energies (BDEs) for 15 acids.These compounds are studied by utilizing the hybrid density functional theory (DFT) (B3LYP,B3PW91,B3P86,PBE1PBE) and the complete basis set (CBS-Q) method in conjunction with the 6-31 lG** basis as DFT methods have been found to have low basis sets sensitivity for small and medium molecules in our previous work.Comparisons between the computational results and the experimental values reveal that CBS-Q method,which can produce reasonable BDEs for some systems in our previous work,seems unable to predict accurate BDEs here.However,the B3P86 calculated results accord very well with the experimental values,within an average absolute error of 2.3 kcal/mol.Thus,B3P86 method is suitable for computing the reliable BDEs of C-COOH bond for carboxylic acid compounds.In addition,the energy gaps between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) of studied compounds are estimated,based on which the relative thermal stabilities of the studied acids are also discussed.
da Silva, E. Lora; Marinopoulos, A. G.; Vieira, R. B. L.; Vilão, R. C.; Alberto, H. V.; Gil, J. M.; Lichti, R. L.; Mengyan, P. W.; Baker, B. B.
2016-07-01
The electronic structure of hydrogen impurity in Lu2O3 was studied by first-principles calculations and muonium spectroscopy. The computational scheme was based on two methods which are well suited to treat defect calculations in f -electron systems: first, a semilocal functional of conventional density-functional theory (DFT) and secondly a DFT+U approach which accounts for the on-site correlation of the 4 f electrons via an effective Hubbard-type interaction. Three different types of stable configurations were found for hydrogen depending upon its charge state. In its negatively charged and neutral states, hydrogen favors interstitial configurations residing either at the unoccupied sites of the oxygen sublattice or at the empty cube centers surrounded by the lanthanide ions. In contrast, the positively charged state stabilized only as a bond configuration, where hydrogen binds to oxygen ions. Overall, the results between the two methods agree in the ordering of the formation energies of the different impurity configurations, though within DFT+U the charge-transition (electrical) levels are found at Fermi-level positions with higher energies. Both methods predict that hydrogen is an amphoteric defect in Lu2O3 if the lowest-energy configurations are used to obtain the charge-transition, thermodynamic levels. The calculations of hyperfine constants for the neutral interstitial configurations show a predominantly isotropic hyperfine interaction with two distinct values of 926 MHz and 1061 MHz for the Fermi-contact term originating from the two corresponding interstitial positions of hydrogen in the lattice. These high values are consistent with the muonium spectroscopy measurements which also reveal a strongly isotropic hyperfine signature for the neutral muonium fraction with a magnitude slightly larger (1130 MHz) from the ab initio results (after scaling with the magnetic moments of the respective nuclei).
Singlet oxygen generation in PUVA therapy studied using electronic structure calculations
Energy Technology Data Exchange (ETDEWEB)
Serrano-Perez, Juan Jose; Olaso-Gonzalez, Gloria; Merchan, Manuela [Instituto de Ciencia Molecular, Universitat de Valencia, Apartado 22085, ES-46071 Valencia (Spain); Serrano-Andres, Luis, E-mail: Luis.Serrano@uv.es [Instituto de Ciencia Molecular, Universitat de Valencia, Apartado 22085, ES-46071 Valencia (Spain)
2009-06-12
The ability of furocoumarins to participate in the PUVA (Psoralen + UV-A) therapy against skin disorders and some types of cancer, is analyzed on quantum chemical grounds. The efficiency of the process relies on its capability to populate its lowest triplet excited state, and then either form adducts with thymine which interfere DNA replication or transfer its energy, generating singlet molecular oxygen damaging the cell membrane in photoactivated tissues. By determining the spin-orbit couplings, shown to be the key property, in the intersystem crossing yielding the triplet state of the furocoumarin, the electronic couplings in the triplet-triplet energy transfer process producing the singlet oxygen, and the reaction rates and lifetimes, the efficiency in the phototherapeutic action of the furocoumarin family is predicted as: khellin < 5-methoxypsoralen (5-MOP) < 8-methoxypsoralen (8-MOP) < psoralen < 4,5',8-trimethylpsoralen (TMP) < 3-carbethoxypsoralen (3-CPS), the latter being the most efficient photosensitizer and singlet oxygen generator.
Liebscher, C H; Freysoldt, C; Dennenwaldt, T; Harzer, T P; Dehm, G
2016-07-12
Metastable Cu-Cr alloy thin films with nominal thickness of 300nm and composition of Cu67Cr33 (at%) are obtained by co-evaporation using molecular beam epitaxy. The microstructure, chemical phase separation and electronic structure are investigated by transmission electron microscopy (TEM). The thin film adopts the body-centered cubic crystal structure and consists of columnar grains with ~50nm diameter. Aberration-corrected scanning TEM in combination with energy dispersive X-ray spectroscopy confirms compositional fluctuations within the grains. Cu- and Cr-rich domains with composition of Cu85Cr15 (at%) and Cu42Cr58 (at%) and domain size of 1-5nm are observed. The alignment of the interface between the Cu- and Cr-rich domains shows a preference for {110}-type habit plane. The electronic structure of the Cu-Cr thin films is investigated by electron energy loss spectroscopy (EELS) and is contrasted to an fcc-Cu reference sample. The experimental EEL spectra are compared to spectra computed by density functional theory. The main differences between bcc-and fcc-Cu are related to differences in van Hove singularities in the electron density of states. In Cu-Cr solid solutions with bcc crystal structure a single peak after the L3-edge, corresponding to a van Hove singularity at the N-point of the first Brillouin zone is observed. Spectra computed for pure bcc-Cu and random Cu-Cr solid solutions with 10at% Cr confirm the experimental observations. The calculated spectrum for a perfect Cu50Cr50 (at%) random structure shows a shift in the van Hove singularity towards higher energy by developing a Cu-Cr d-band that lies between the delocalized d-bands of Cu and Cr.
Revised self-consistent continuum solvation in electronic-structure calculations
Andreussi, Oliviero; Marzari, Nicola
2011-01-01
The solvation model proposed by Fattebert and Gygi [Journal of Computational Chemistry 23, 662 (2002)] and Scherlis et al. [Journal of Chemical Physics 124, 074103 (2006)] is reformulated, overcoming some of the numerical limitations encountered and extending its range of applicability. We first recast the problem in terms of induced polarization charges that act as a direct mapping of the self-consistent continuum dielectric; this allows to define a functional form for the dielectric that is well behaved both in the high-density region of the nuclear charges and in the low-density region where the electronic wavefunctions decay into the solvent. Second, we outline an iterative procedure to solve the Poisson equation for the quantum fragment embedded in the solvent that does not require multi-grid algorithms, is trivially parallel, and can be applied to any Bravais crystallographic system. Last, we capture some of the non-electrostatic or cavitation terms via a combined use of the quantum volume and quantum s...
Kinetic Formulation of the Kohn-Sham Equations for ab initio Electronic Structure Calculations
Mendoza, M; Herrmann, H J
2013-01-01
We introduce a new approach to density functional theory based on kinetic theory, showing that the Kohn-Sham equations can be derived as a macroscopic limit of a suitable Boltzmann kinetic equation in the limit of small mean free path versus the typical scale of density gradients (Chapman-Enskog expansion). To derive the approach, we first write the Schr\\"odinger equation as a special case of a Boltzmann equation for a gas of quasi-particles, with the potential playing the role of an external source that generates and destroys particles, so as to drive the system towards the ground state. The ions are treated as classical particles, using the Born-Oppenheimer dynamics, or by imposing concurrent evolution with the electronic orbitals. In order to provide quantitative support to our approach, we implement a discrete (lattice) model and compute, the exchange and correlation energies of simple atoms, and the geometrical configuration of the methane molecule. Excellent agreement with values in the literature is fo...
Energy Technology Data Exchange (ETDEWEB)
Kostko, Oleg; Bravaya, Ksenia; Krylov, Anna; Ahmed, Musahid
2009-12-14
We report a combined theoretical and experimental study of ionization of cytosine monomers and dimers. Gas-phase molecules are generated by thermal vaporization of cytosine followed by expansion of the vapor in a continuous supersonic jet seeded in Ar. The resulting species are investigated by single photon ionization with tunable vacuum-ultraviolet (VUV) synchrotron radiation and mass analyzed using reflectron mass spectrometry. Energy onsets for the measured photoionization efficiency (PIE) spectra are 8.60+-0.05 eV and 7.6+-0.1 eV for the monomer and the dimer, respectively, and provide an estimate for the adiabatic ionization energies (AIE). The first AIE and the ten lowest vertical ionization energies (VIEs) for selected isomers of cytosine dimer computed using equation-of-motion coupled-cluster (EOM-IP-CCSD) method are reported. The comparison of the computed VIEs with the derivative of the PIE spectra, suggests that multiple isomers of the cytosine dimer are present in the molecular beam. The calculations reveal that the large red shift (0.7 eV) of the first IE of the lowest-energy cytosine dimer is due to strong inter-fragment electrostatic interactions, i.e., the hole localized on one of the fragments is stabilized by the dipole moment of the other. A sharp rise in the CH+ signal at 9.20+-0.05 eV is ascribed to the formation of protonated cytosine by dissociation of the ionized dimers. The dominant role of this channel is supported by the computed energy thresholds for the CH+ appearance and the barrierless or nearly barrierless ionization-induced proton transfer observed for five isomers of the dimer.
Accurate variational electronic structure calculations with the density matrix renormalization group
Wouters, Sebastian
2014-01-01
During the past 15 years, the density matrix renormalization group (DMRG) has become increasingly important for ab initio quantum chemistry. The underlying matrix product state (MPS) ansatz is a low-rank decomposition of the full configuration interaction tensor. The virtual dimension of the MPS controls the size of the corner of the many-body Hilbert space that can be reached. Whereas the MPS ansatz will only yield an efficient description for noncritical one-dimensional systems, it can still be used as a variational ansatz for other finite-size systems. Rather large virtual dimensions are then required. The two most important aspects to reduce the corresponding computational cost are a proper choice and ordering of the active space orbitals, and the exploitation of the symmetry group of the Hamiltonian. By taking care of both aspects, DMRG becomes an efficient replacement for exact diagonalization in quantum chemistry. DMRG and Hartree-Fock theory have an analogous structure. The former can be interpreted a...
Enkovaara, J; Rostgaard, C; Mortensen, J J; Chen, J; Dułak, M; Ferrighi, L; Gavnholt, J; Glinsvad, C; Haikola, V; Hansen, H A; Kristoffersen, H H; Kuisma, M; Larsen, A H; Lehtovaara, L; Ljungberg, M; Lopez-Acevedo, O; Moses, P G; Ojanen, J; Olsen, T; Petzold, V; Romero, N A; Stausholm-Møller, J; Strange, M; Tritsaris, G A; Vanin, M; Walter, M; Hammer, B; Häkkinen, H; Madsen, G K H; Nieminen, R M; Nørskov, J K; Puska, M; Rantala, T T; Schiøtz, J; Thygesen, K S; Jacobsen, K W
2010-06-30
Electronic structure calculations have become an indispensable tool in many areas of materials science and quantum chemistry. Even though the Kohn-Sham formulation of the density-functional theory (DFT) simplifies the many-body problem significantly, one is still confronted with several numerical challenges. In this article we present the projector augmented-wave (PAW) method as implemented in the GPAW program package (https://wiki.fysik.dtu.dk/gpaw) using a uniform real-space grid representation of the electronic wavefunctions. Compared to more traditional plane wave or localized basis set approaches, real-space grids offer several advantages, most notably good computational scalability and systematic convergence properties. However, as a unique feature GPAW also facilitates a localized atomic-orbital basis set in addition to the grid. The efficient atomic basis set is complementary to the more accurate grid, and the possibility to seamlessly switch between the two representations provides great flexibility. While DFT allows one to study ground state properties, time-dependent density-functional theory (TDDFT) provides access to the excited states. We have implemented the two common formulations of TDDFT, namely the linear-response and the time propagation schemes. Electron transport calculations under finite-bias conditions can be performed with GPAW using non-equilibrium Green functions and the localized basis set. In addition to the basic features of the real-space PAW method, we also describe the implementation of selected exchange-correlation functionals, parallelization schemes, ΔSCF-method, x-ray absorption spectra, and maximally localized Wannier orbitals.
Energy Technology Data Exchange (ETDEWEB)
Enkovaara, J [CSC-IT Center for Science Ltd, PO Box 405 FI-02101 Espoo (Finland); Rostgaard, C; Mortensen, J J; Chen, J; Dulak, M; Glinsvad, C; Hansen, H A; Larsen, A H; Moses, P G; Petzold, V [Center for Atomic-scale Materials Design, Department of Physics, Technical University of Denmark, DK-2800 Kongens Lyngby (Denmark); Ferrighi, L; Kristoffersen, H H [Interdisciplinary Nanoscience Center (iNANO) and Department of Physics and Astronomy, Aarhus University, DK-8000 Aarhus C (Denmark); Gavnholt, J; Olsen, T [Danish National Research Foundation' s Center for Individual Nanoparticle Functionality (CINF), Technical University of Denmark, DK-2800 Kongens Lyngby (Denmark); Haikola, V; Lehtovaara, L [Department of Applied Physics, Aalto University School of Science and Technology, PO Box 11000, FIN-00076 Aalto, Espoo (Finland); Kuisma, M; Ojanen, J [Department of Physics, Tampere University of Technology, PO Box 692, FI-33101 Tampere (Finland); Ljungberg, M [FYSIKUM, Stockholm University, Albanova University Center, SE-10691 Stockholm (Sweden); Lopez-Acevedo, O [Departments of Physics and Chemistry, Nanoscience Center, University of Jyvaeskylae, PO Box 35 (YFL), FI-40014 (Finland)
2010-06-30
Electronic structure calculations have become an indispensable tool in many areas of materials science and quantum chemistry. Even though the Kohn-Sham formulation of the density-functional theory (DFT) simplifies the many-body problem significantly, one is still confronted with several numerical challenges. In this article we present the projector augmented-wave (PAW) method as implemented in the GPAW program package (https://wiki.fysik.dtu.dk/gpaw) using a uniform real-space grid representation of the electronic wavefunctions. Compared to more traditional plane wave or localized basis set approaches, real-space grids offer several advantages, most notably good computational scalability and systematic convergence properties. However, as a unique feature GPAW also facilitates a localized atomic-orbital basis set in addition to the grid. The efficient atomic basis set is complementary to the more accurate grid, and the possibility to seamlessly switch between the two representations provides great flexibility. While DFT allows one to study ground state properties, time-dependent density-functional theory (TDDFT) provides access to the excited states. We have implemented the two common formulations of TDDFT, namely the linear-response and the time propagation schemes. Electron transport calculations under finite-bias conditions can be performed with GPAW using non-equilibrium Green functions and the localized basis set. In addition to the basic features of the real-space PAW method, we also describe the implementation of selected exchange-correlation functionals, parallelization schemes, {Delta}SCF-method, x-ray absorption spectra, and maximally localized Wannier orbitals. (topical review)
Role of anion doping on electronic structure and magnetism of GdN by first principles calculations
Zhang, Xuejing
2014-01-01
We have investigated the electronic structure and magnetism of anion doped GdN1-yXy (X = B, C, O, F, P, S and As) systems by first-principles calculations based on density functional theory. GdN 1-yXy systems doped by O, C, F, P, and S atoms are more stable than those doped by B and As atoms because of relatively high binding energies. The anion doping and the N defect states modify the density of states at the Fermi level, resulting in a decrease in spin polarization and a slight increase in the magnetic moment at the Gd and N sites. © 2014 The Royal Society of Chemistry.
Bannikov, V. V.; Shein, I. R.; Ivanovskii, A. L.
2012-01-01
The structural, elastic, magnetic and electronic properties of the layered tetragonal phase KCo 2Se 2 have been examined in details by means of the first-principles calculations and analyzed in comparison with the isostructural KFe 2Se 2 as the parent phase for the newest group of ternary superconducting iron-chalcogenide materials. Our data show that KCo 2Se 2 should be characterized as a quasi-two-dimensional ferromagnetic metal with highly anisotropic inter-atomic bonding owing to mixed ionic, covalent, and metallic contributions inside [Co 2Se 2] blocks, and with ionic bonding between the adjacent [Co 2Se 2] blocks and K sheets. This material should behave in a brittle manner, adopt enhanced elastic anisotropy rather in compressibility than in shear, and should show very low hardness.
Curie temperature of GaMnN and GaMnAs from LDA-SIC electronic structure calculations
Energy Technology Data Exchange (ETDEWEB)
Toyoda, Masayuki; Sato, Kazunori; Katayama-Yoshida, Hiroshi [Department of Computational Nanomaterials Design, Institute of Scientific and Industrial Research, Osaka University, 8-1 Mihogaoka, Ibaraki, Osaka 567-0047 (Japan); Akai, Hisazumi [Department of Physics, Graduate School of Science, Osaka University, 1-1 Machikaneyama, Toyonaka, Osaka 560-0043 (Japan)
2006-07-01
We present the electronic structures, magnetic exchange interactions and Curie temperature (T{sub C}) of GaMnN and GaMnAs calculated by self-interaction-corrected local-density approximation (LDA-SIC). In GaMnAs, the LDA-SIC results of T{sub C} do not differ so much from the LDA results. Both the LDA and LDA-SIC values are in a good agreement with the experimental data. In GaMnN, on the other hand, the ferromagnetic exchange interactions are enhanced due to the suppression of antiferromagnetic super-exchange interaction, resulting in T{sub C} higher than the LDA results. (copyright 2006 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)
Banerjee, Amartya S.; Lin, Lin; Hu, Wei; Yang, Chao; Pask, John E.
2016-10-01
The Discontinuous Galerkin (DG) electronic structure method employs an adaptive local basis (ALB) set to solve the Kohn-Sham equations of density functional theory in a discontinuous Galerkin framework. The adaptive local basis is generated on-the-fly to capture the local material physics and can systematically attain chemical accuracy with only a few tens of degrees of freedom per atom. A central issue for large-scale calculations, however, is the computation of the electron density (and subsequently, ground state properties) from the discretized Hamiltonian in an efficient and scalable manner. We show in this work how Chebyshev polynomial filtered subspace iteration (CheFSI) can be used to address this issue and push the envelope in large-scale materials simulations in a discontinuous Galerkin framework. We describe how the subspace filtering steps can be performed in an efficient and scalable manner using a two-dimensional parallelization scheme, thanks to the orthogonality of the DG basis set and block-sparse structure of the DG Hamiltonian matrix. The on-the-fly nature of the ALB functions requires additional care in carrying out the subspace iterations. We demonstrate the parallel scalability of the DG-CheFSI approach in calculations of large-scale two-dimensional graphene sheets and bulk three-dimensional lithium-ion electrolyte systems. Employing 55 296 computational cores, the time per self-consistent field iteration for a sample of the bulk 3D electrolyte containing 8586 atoms is 90 s, and the time for a graphene sheet containing 11 520 atoms is 75 s.
Shi, Haifeng; Lan, Benyue; Zhang, Chengliang; Ye, Enjia; Nie, Yanguang; Bian, Baoan
2016-10-01
The influences of a series of anion doping on the electronic structures of sodium niobate (NaNbO3) have been systematically investigated by density functional theory (DFT) calculations with the hybrid B3LYP functional. As for B(C,P)-doped NaNbO3, the isolated B 2p (C 2p, P 3p) states were formed above the valence band maximum (VBM) of NaNbO3, which were too weak to mix with O 2p states and thus produced band gap narrowing. While the band gap of NaNbO3 was slightly narrowed after F doping. As for S-doped NaNbO3, the S 3p states mixed with O 2p states well and thus reduced the band gap energy. According to the calculation results, we tentatively put forward that S doping would be appropriate for single anion doping NaNbO3, while the B(C,P) elements would be suitable candidates for co-doping NaNbO3.
Joshi, Bhawani Datt; Srivastava, Anubha; Honorato, Sara Braga; Tandon, Poonam; Pessoa, Otília Deusdênia Loiola; Fechine, Pierre Basílio Almeida; Ayala, Alejandro Pedro
2013-09-01
Oncocalyxone A (C17H18O5) is the major secondary metabolite isolated from ethanol extract from the heartwood of Auxemma oncocalyx Taub popularly known as “pau branco”. Oncocalyxone A (Onco A) has many pharmaceutical uses such as: antitumor, analgesic, antioxidant and causative of inhibition of platelet activation. We have performed the optimized geometry, total energy, conformational study, molecular electrostatic potential mapping, frontier orbital energy gap and vibrational frequencies of Onco A employing ab initio Hartree-Fock (HF) and density functional theory (DFT/B3LYP) method with 6-311++G(d, p) basis set. Stability of the molecule arising from hyperconjugative interactions and/or charge delocalization has been analyzed using natural bond orbital (NBO) analysis. UV-vis spectrum of the compound was recorded in DMSO and MeOH solvent. The TD-DFT calculations have been performed to explore the influence of electronic absorption spectra in the gas phase, as well as in solution environment using IEF-PCM and 6-31G basis set. The 13C NMR chemical shifts have been calculated with the B3LYP/6-311++G(d, p) basis set and compared with the experimental values. These methods have been used as tools for structural characterization of Onco A.
Joshi, Bhawani Datt; Srivastava, Anubha; Honorato, Sara Braga; Tandon, Poonam; Pessoa, Otília Deusdênia Loiola; Fechine, Pierre Basílio Almeida; Ayala, Alejandro Pedro
2013-09-01
Oncocalyxone A (C17H18O5) is the major secondary metabolite isolated from ethanol extract from the heartwood of Auxemma oncocalyx Taub popularly known as "pau branco". Oncocalyxone A (Onco A) has many pharmaceutical uses such as: antitumor, analgesic, antioxidant and causative of inhibition of platelet activation. We have performed the optimized geometry, total energy, conformational study, molecular electrostatic potential mapping, frontier orbital energy gap and vibrational frequencies of Onco A employing ab initio Hartree-Fock (HF) and density functional theory (DFT/B3LYP) method with 6-311++G(d,p) basis set. Stability of the molecule arising from hyperconjugative interactions and/or charge delocalization has been analyzed using natural bond orbital (NBO) analysis. UV-vis spectrum of the compound was recorded in DMSO and MeOH solvent. The TD-DFT calculations have been performed to explore the influence of electronic absorption spectra in the gas phase, as well as in solution environment using IEF-PCM and 6-31G basis set. The (13)C NMR chemical shifts have been calculated with the B3LYP/6-311++G(d,p) basis set and compared with the experimental values. These methods have been used as tools for structural characterization of Onco A.
Shlykov, Sergey A.; Phien, Tran D.; Gao, Yan; Weber, Peter M.
2017-03-01
Molecular structure and conformational behavior of N-phenylpiperidine (NPhP) were investigated by synchronous gas-phase electron diffraction/mass spectrometry (GED/MS) and quantum chemistry. Due to influence of steric repulsion and hyperconjugation, NPhP may exist in two conformers, equatorial and axial chair forms. Both experiment and theoretical calculations suggest a C1 symmetry of the conformers, with the plane perpendicular to the phenyl group turned by ca. 30-40° (equatorial) and 0-20° (axial) about the plane perpendicular to the piperidine ring symmetry plane. According to the QC calculations, NPhP may exist as two conformers, equatorial and axial, with a ratio of Eq:Ax = 92:8 (B3LYP), 87:13 (B3LYP-GD3), 84:16 (M06-2X), 83:17 (MP2/6-311G**) and 76:24% (MP2/cc-pVTZ). Except for the latter, these values are in good agreement with the experimental GED data of 90(10):10(10)%. A comparative analysis of similar compounds, phenylcyclohexane and 1-phenylheterocyclohexanes, was performed. Conformational properties depend on the CPhsbnd X bond distance and hyperconjugation between the phenyl ring and the lone pair on the heteroatom. The contribution of the axial form of 1-phenylcyclohexane derivatives increases in the series of the heteroatom X in the cyclohexane ring: C → N → Si → P.
Electronics reliability calculation and design
Dummer, Geoffrey W A; Hiller, N
1966-01-01
Electronics Reliability-Calculation and Design provides an introduction to the fundamental concepts of reliability. The increasing complexity of electronic equipment has made problems in designing and manufacturing a reliable product more and more difficult. Specific techniques have been developed that enable designers to integrate reliability into their products, and reliability has become a science in its own right. The book begins with a discussion of basic mathematical and statistical concepts, including arithmetic mean, frequency distribution, median and mode, scatter or dispersion of mea
Chelli, S.; Meradji, H.; Amara Korba, S.; Ghemid, S.; El Haj Hassan, F.
2014-12-01
The structural, electronic thermodynamic and thermal properties of BaxSr1-xTe ternary mixed crystals have been studied using the ab initio full-potential linearized augmented plane wave (FP-LAPW) method within density functional theory (DFT). In this approach, the Perdew-Burke-Ernzerhof-generalized gradient approximation (PBE-GGA) was used for the exchange-correlation potential. Moreover, the recently proposed modified Becke Johnson (mBJ) potential approximation, which successfully corrects the band-gap problem was also used for band structure calculations. The ground-state properties are determined for the cubic bulk materials BaTe, SrTe and their mixed crystals at various concentrations (x = 0.25, 0.5 and 0.75). The effect of composition on lattice constant, bulk modulus and band gap was analyzed. Deviation of the lattice constant from Vegard's law and the bulk modulus from linear concentration dependence (LCD) were observed for the ternary BaxSr1-xTe alloys. The microscopic origins of the gap bowing were explained by using the approach of Zunger and co-workers. On the other hand, the thermodynamic stability of these alloys was investigated by calculating the excess enthalpy of mixing, ΔHm as well as the phase diagram. It was shown that these alloys are stable at high temperature. Thermal effects on some macroscopic properties of BaxSr1-xTe alloys were investigated using the quasi-harmonic Debye model, in which the phononic effects are considered.
Electronic and magnetic structure of BaCoO{sub 2} as obtained from LSDA and LSDA+U calculations
Energy Technology Data Exchange (ETDEWEB)
Nazir, S.; Zhu, Z.Y.; Pulikkotil, J.J. [KAUST, PSE Division, 23955-6900 Thuwal (Saudi Arabia); Schwingenschloegl, U., E-mail: udo.schwingenschlogl@kaust.edu.s [KAUST, PSE Division, 23955-6900 Thuwal (Saudi Arabia)
2011-03-21
Density functional theory is used to study the structural, electronic, and magnetic properties of BaCoO{sub 2}. Structural relaxation for different collinear magnetic configurations points to a remarkable magneto-elastic coupling in BaCoO{sub 2}. Although we obtain several stable long range ordered magnetic structures, ferromagnetism is energetically favorable in the case of the LSDA method. In contrast, for the LSDA+U method antiferromagnetic ordering is found to be favorable. - Highlights: Strong magneto-elastic coupling. Local density approximation yields half-metallic ferromagnetic state. Onsite electron-electron interaction induces antiferromagnetism.
Institute of Scientific and Technical Information of China (English)
LIU Zhilin; LIN Cheng; LIU Yan; GUO Yanchang
2005-01-01
Based on the phase transformations and strengthening mechanisms during roiling, the strength increments △σb under different strengthening mechanisms are calculated with the covalent electron number nA of the strongest bond in phase cells of alloys and the interface electron density difference △ρ matching the interface stress in alloys. The calculation method of the finishing rolling yield strength is proposed, and it is integrated with the proposed calculation formulas of strength of non quenched-tempered steel. Therefore,the general formulas to simultaneously calculate both the finishing rolling strength and the yield strength of the continuous casting-rolling and non quenched-tempered steel are given. Taken the pipeline steel X70 as an example, the predictions of properties and technological parameters are performed before production or online.
Energy Technology Data Exchange (ETDEWEB)
Guemou, M., E-mail: guemoumhamed7@gmail.com [Engineering Physics Laboratory, University Ibn Khaldoun of Tiaret, BP 78-Zaaroura, Tiaret 14000 (Algeria); Bouhafs, B. [Modelling and Simulation in Materials Science Laboratory, Physics Department, University of Sidi Bel-Abbes, 22000 Sidi Bel-Abbes (Algeria); Abdiche, A. [Applied Materials Laboratory, Research Center, University of Sidi Bel Abbes, 22000 Sidi Bel Abbes (Algeria); Khenata, R. [Laboratoire de Physique Quantique et de Modelisation Mathematique (LPQ3M), Departement de Technologie, Universite de Mascara, 29000 Mascara (Algeria); Al Douri, Y. [Institute of Nano Electronic Engineering, Universiti Malaysia Perlis, Perlis (Malaysia); Bin Omran, S. [Department of Physics and Astronomy, Faculty of Science, King Saud University, P.O. Box 2455, Riyadh 11451 (Saudi Arabia)
2012-04-15
Density functional calculations are performed to study the structural, electronic and optical properties of technologically important B{sub x}Ga{sub 1-x}As ternary alloys. The calculations are based on the total-energy calculations within the full-potential augmented plane-wave (FP-LAPW) method. For exchange-correlation potential, local density approximation (LDA) and the generalized gradient approximation (GGA) have been used. The structural properties, including lattice constants, bulk modulus and their pressure derivatives, are in very good agreement with the available experimental and theoretical data. The electronic band structure, density of states for the binary compounds and their ternary alloys are given. The dielectric function and the refractive index are also calculated using different models. The obtained results compare very well with previous calculations and experimental measurements.
Institute of Scientific and Technical Information of China (English)
ZHOU Jing; REN Xiao-Min; HUANG Yong-Qing; WANG Qi; HUANG Hui
2008-01-01
We investigate the electronic structures of new semiconductor alloys BxGa1-x As and Tlx Ga1-x As, employing first-principles calculations within the density-functional theory and the generalized gradient approximation.The calculation results indicate that alloying a small Tl content with GaAs will produce larger modifications of the band structures compared to B. A careful investigation of the internal lattice structure relaxation shows that significant bond-length relaxations takes place in both the alloys, and it turns out that difference between the band-gap bowing behaviours for B and Tl stems from the different impact of atomic relaxation on the electronic structure. The relaxed structure yields electronic-structure results, which are in good agreement with the experimental data. Finally, a comparison of formation enthalpies indicates that the production Tlx Ga1-x As with Tl concentration of at least 8% is possible.
2008-01-01
The molecular structures of methylphosphine (CH3PH2) and methylphosphine-borane (CH3PH2·BH3) have been determined from gas-phase electron diffraction data and rotational constants, employing the SARACEN method. The experimental geometric parameters generally showed a good agreement with those obtained using ab initio calculations and previous microwave spectroscopy studies. In order to assess the accuracy of the calculated structures a range of ab initio methods were used, including the CCSD(...
Andrews, Lester; Wang, Xuefeng; Gong, Yu; Kushto, Gary P; Vlaisavljevich, Bess; Gagliardi, Laura
2014-07-17
Reactions of laser-ablated U atoms with N2 molecules upon codeposition in excess argon or neon at 4 K gave intense NUN and weak UN absorptions. Annealing produced progressions of new absorptions for the UN2(N2)1,2,3,4,5 and UN(N2)1,2,3,4,5,6 complexes. The neon-to-argon matrix shift decreases with increasing NN ligation and therefore the number of noble gas atoms left in the primary coordination sphere around the NUN molecule. Small matrix shifts are observed when the secondary coordination layers around the primary UN2(N2)1,2,3,4,5 and UN(N2)1,2,3,4,5,6 complexes are changed from neon-to-argon to nitrogen. Electronic structure, energy, and frequency calculations provide support for the identification of these complexes and the characterization of the N≡U≡N and U≡N core molecules as terminal uranium nitrides. Codeposition of U with pure nitrogen produced the saturated U(NN)7 complex, which UV irradiation converted to the NUN(NN)5 complex with slightly lower frequencies than found in solid argon.
Energy Technology Data Exchange (ETDEWEB)
Olsson, Paer
2004-04-01
The efficiency of fast neutron reactors, such as for fusion, breeding and transmutation, depend strongly on the neutron radiation resistance of the materials used in the reactors. The binary Fe-Cr alloy, which has many attractive properties in this regard, is the base for the best steels of today which are, however, still not up to the required standards. Therefore, substantial effort has been devoted to finding new materials that can cope with the demands better. Experimental studies must be complemented with extensive theoretical modelling in order to understand the effects that different alloying elements has on the resistance properties of materials. To this end, the first steps of multi-scale modelling has been taken, starting out with ab initio calculations of the electronic structure of the complete concentration range range of the disordered binary Fe-C alloy. The mixing enthalpy of Fe-Cr has been quantitatively predicted and has, together with data from literature, been used in order to fit two sets of interatomic potentials for the purpose of simulating defect evolution with molecular dynamics and kinetic Monte-Carlo codes. These dedicated Fe-Cr alloy potentials are new and represent important additions to the pure element potentials that can be found in literature.
Electronic Structures of S/C-Doped TiO2 Anatase (101 Surface: First-Principles Calculations
Directory of Open Access Journals (Sweden)
Qili Chen
2014-01-01
Full Text Available The electronic structures of sulfur (S or carbon (C-doped TiO2 anatase (101 surfaces have been investigated by density functional theory (DFT plane-wave pseudopotential method. The general gradient approximation (GGA + U (Hubbard coefficient method has been adopted to describe the exchange-correlation effects. All the possible doping situations, including S/C dopants at lattice oxygen (O sites (anion doping, S/C dopants at titanium (Ti sites (cation doping, and the coexisting of anion and cation doping, were studied. By comparing the formation energies, it was found that the complex of anion and cation doping configuration forms easily in the most range of O chemical potential for both S and C doping. The calculated density of states for various S/C doping systems shows that the synergistic effects of S impurities at lattice O and Ti sites lead a sharp band gap narrowing of 1.35 eV for S-doped system comparing with the pure TiO2 system.
Energy Technology Data Exchange (ETDEWEB)
Benrekia, A.R., E-mail: benrekia.ahmed@yahoo.com [Faculty of Science and Technology, University of Medea (Algeria); Benkhettou, N. [Laboratoire des Materiaux Magnetiques, Faculte des Sciences, Universite Djillali Liabes de Sidi Bel Abbes (Algeria); Nassour, A. [Laboratoire de Cristallographie, Resonance Magnetique et Modelisations (CRM2, UMR CNRS 7036) Institut Jean Barriol, Nancy Universite BP 239, Boulevard des Aiguillettes, 54506 Vandoeuvre-les-Nancy (France); Driz, M. [Applied Material Laboratory (AML), Electronics Department, University of Sidi bel Abbes (DZ 22000) (Algeria); Sahnoun, M. [Laboratoire de Physique Quantique de la Matiere et Modelisations Mathematique (LPQ3M), Faculty of Science and Technology,University of Mascara (Algeria); Lebegue, S. [Laboratoire de Cristallographie, Resonance Magnetique et Modelisations (CRM2, UMR CNRS 7036) Institut Jean Barriol, Nancy Universite BP 239, Boulevard des Aiguillettes, 54506 Vandoeuvre-les-Nancy (France)
2012-07-01
We present first-principles VASP calculations of the structural, electronic, vibrational, and optical properties of paraelectric SrTiO{sub 3} and KTaO{sub 3}. The ab initio calculations are performed in the framework of density functional theory with different exchange-correlation potentials. Our calculated lattice parameters, elastic constants, and vibrational frequencies are found to be in good agreement with the available experimental values. Then, the bandstructures are calculated with the GW approximation, and the corresponding band gap is used to obtain the optical properties of SrTiO{sub 3} and KTaO{sub 3}.
Zhao, Zhengji
We study the reduced density matrix method, a variational approach for electronic structure calculations based on the two-body reduced density matrix. This method minimizes the ground state energy with respect to the two-body reduced density matrix subject to some conditions which it must satisfy, known as N-representability conditions. The resulting optimization problem is a semidefinite program, a convex optimization problem for which computational methods have greatly advanced during the past decade. Two significant advances are reported in this thesis. First, we formulate the reduced density matrix method using the dual formulation of semidefinite programming instead of the previously-used primal one; this results in substantial computational savings and makes it possible to study larger systems than was done previously. Second, in addition to the previously-used P, Q and G conditions we investigate a pair of positive semidefinite conditions that has a three-index form; we call them the T1 and T2 conditions. We find that the inclusion of the T1 and T2 conditions gives a significant improvement over results previously obtained using only the P, Q and G conditions; and provides in all cases we have studied (47 molecules) more accurate results than other more familiar methods: Hartree-Fork; 2nd order Moller-Plesset method (MP2), singly and doubly substituted configuration interaction (SDCI), quadratic configuration interaction including single and double substitutions (QCISD), Brueckner doubles (with triples) (BD(T)) and coupled cluster singles and doubles with perturbational treatment of triples (CCSD(T)).
Agrawal, P M; Malshe, M; Narulkar, R; Raff, L M; Hagan, M; Bukkapatnum, S; Komanduri, R
2009-02-05
Previous methods proposed for obtaining analytic potential-energy surfaces (PES) from ab initio electronic structure calculations are not self-starting. They generally require that the sampling of configuration space important in the reaction dynamics of the process being investigated be initiated by using chemical intuition or a previously developed semiempirical potential-energy surface. When the system under investigation contains four or more atoms undergoing three- and four-center reactions in addition to bond scission processes, obtaining a sufficiently converged initial sampling can be very difficult due to the extremely large volume of configuration space that is important in the reaction dynamics. It is shown that by combining direct dynamics (DD) with previously reported molecular dynamics (MD), novelty sampling (NS), and neural network (NN) methods, an analytical surface suitable for MD computations for large systems may be obtained. Application of the method to the investigation of N-O bond scission and cis-trans isomerization reactions of HONO followed by comparison of the resulting neural network potential-energy surface to one obtained by using a semiempirical potential to initiate the sampling shows that the two potential surfaces are the same within the fitting accuracy of the surfaces. It is concluded that the combination of direct dynamics, molecular dynamics, novelty sampling, and neural network fitting provides a self-starting, robust, and accurate DD/MD/NS/NN method for the execution of first-principles, ab initio, molecular dynamics studies in systems containing four or more atoms which are undergoing simultaneous two-, three-, and four-center reactions.
rehman Hashmi, Muhammad Raza ur; Zafar, Muhammad; Shakil, M.; Sattar, Atif; Ahmed, Shabbir; Ahmad, S. A.
2016-11-01
First-principles calculations by means of the full-potential linearized augmented plane wave method using the generalized gradient approximation with correlation effect correction (GGA+U) within the framework of spin polarized density functional theory (DFT+U) are used to study the structural, electronic, and magnetic properties of cubic perovskite compounds RbXF3 (X = Mn, V, Co, and Fe). It is found that the calculated structural parameters, i.e., lattice constant, bulk modulus, and its pressure derivative are in good agreement with the previous results. Our results reveal that the strong spin polarization of the 3d states of the X atoms is the origin of ferromagnetism in RbXF3. Cohesive energies and the magnetic moments of RbXF3 have also been calculated. The calculated electronic properties show the half-metallic nature of RbCoF3 and RbFeF3, making these materials suitable for spintronic applications.
Ksenafontov, Denis N.; Moiseeva, Natalia F.; Khristenko, Lyudmila V.; Karasev, Nikolai M.; Shishkov, Igor F.; Vilkov, Lev V.
2010-12-01
The geometric structure of piracetam was studied by quantum chemical calculations (DFT and ab initio), gas electron diffraction (GED), and FTIR spectroscopy. Two stable mirror symmetric isomers of piracetam were found. The conformation of pyrrolidine ring is an envelope in which the C4 atom deviates from the ring plane, the angle between the planes (C3 sbnd C4 sbnd C5) and (C2 sbnd C3 sbnd C5) is 154.1°. The direction of the deviation is the same as that of the side acetamide group. The piracetam molecule is stabilized in the gas phase by an intramolecular hydrogen bond between the N9H 2 group and the oxygen O6, bonded to C2. The principal structural parameters ( re, Å and ∠e, degrees; uncertainties are 3 σLS values) were found to be: r(С3 sbnd С4) = 1.533(1), r(C4 sbnd C5) = 1.540(1), r(N1 sbnd C5) = 1.456(1), r(C2 sbnd C3) = 1.520(1), r(N1 sbnd C7) = 1.452(1), r(C7 sbnd C8) = 1.537(1), r(N1 sbnd C2) = 1.365(2), r(C8 sbnd N9) = 1.360(2), r(C2 dbnd O6) = 1.229(1), r(C8 dbnd O10) = 1.221(1), ∠C2 sbnd N1 sbnd C5 = 113.4(6), ∠N1 sbnd C2 sbnd C3 = 106.9(6), ∠N1 sbnd C7 sbnd C8 = 111.9(6), ∠C7 sbnd C8 sbnd N9 = 112.5(6), ∠N1 sbnd C2 sbnd O6 = 123.0(4), ∠C3 sbnd N1 sbnd C7 = 120.4(4), ∠C7 sbnd C8 sbnd O10 = 120.2(4), ∠C5 sbnd N1 sbnd C2 sbnd O6 = 170(6), ∠C3 sbnd C2 sbnd N1 sbnd C7 = 178(6), ∠C2 sbnd N1 sbnd C7 sbnd C8 = 84.2, ∠N1 sbnd C7 sbnd C8 sbnd O10 = 111.9.
Wetsel, Grover C., Jr.
1978-01-01
Calculates the energy-band structure of noninteracting electrons in a one-dimensional crystal using exact and approximate methods for a rectangular-well atomic potential. A comparison of the two solutions as a function of potential-well depth and ratio of lattice spacing to well width is presented. (Author/GA)
Jaeger, C.R.; Debowski, M.A.; Manners, I.; Vancso, G.J.
1999-01-01
Ab initio molecular orbital calculations at the MP2/6-31G* level of theory have been used to study the molecular geometry, electronic structure, and the thermal stability of six-membered phosphazene and heterophosphazene rings. The studies included the phosphazene ring [NPCl2]3, the carbophosphazene
Electronic and magnetic structure of BaCoO2 as obtained from LSDA and LSDA+U calculations
Nazir, Safdar
2011-03-01
Density functional theory is used to study the structural, electronic, and magnetic properties of BaCoO2. Structural relaxation for different collinear magnetic configurations points to a remarkable magneto-elastic coupling in BaCoO2. Although we obtain several stable long range ordered magnetic structures, ferromagnetism is energetically favorable in the case of the LSDA method. In contrast, for the LSDA+U method antiferromagnetic ordering is found to be favorable. © 2011 Elsevier B.V. All rights reserved.
Energy Technology Data Exchange (ETDEWEB)
Verchenko, V.Yu.; Likhanov, M.S.; Kirsanova, M.A. [Department of Chemistry, Lomonosov Moscow State University, Moscow 119991 (Russian Federation); Gippius, A.A; Tkachev, A.V.; Gervits, N.E. [Faculty of Physics, Lomonosov Moscow State University, Moscow 119991 (Russian Federation); A.V. Shubnikov Institute of Crystallography, Moscow 119333 (Russian Federation); Galeeva, A.V. [Faculty of Physics, Lomonosov Moscow State University, Moscow 119991 (Russian Federation); Buettgen, N.; Kraetschmer, W. [Institut fuer Physik, University of Augsburg, Augsburg D-86135 (Germany); Lue, C.S. [Department of Physics, National Cheng Kung University, Tainan 70101, Taiwan (China); Okhotnikov, K.S. [Materials and Environmental Chemistry, Stockholm University, Stockholm (Sweden); Shevelkov, A.V., E-mail: shev@inorg.chem.msu.ru [Department of Chemistry, Lomonosov Moscow State University, Moscow 119991 (Russian Federation)
2012-10-15
Unlimited solid solution Fe{sub 1-x}Co{sub x}Ga{sub 3} was prepared from Ga flux. Its crystal structure was refined for Fe{sub 0.5}Co{sub 0.5}Ga{sub 3} (P4{sub 2}/mnm, a=6.2436(9), c=6.4654(13), Z=4) and showed no ordering of the metal atoms. A combination of the electronic band structure calculations within the density functional theory (DFT) approach and {sup 69,71}Ga nuclear quadrupole resonance (NQR) spectroscopy clearly shows that the Fe-Fe and Co-Co dumbbells are preferred to the Fe-Co dumbbells in the crystals structure. The band structure features a band gap of about 0.4 eV, with the Fermi level crossing peaks of a substantial density of electronic states above the gap for x>0. The solid solution is metallic for x>0.025. The study of the nuclear spin-lattice relaxation shows that the rate of the relaxation, 1/T{sub 1}, is very sensitive to the Co concentration and correlates well with the square of the density of states at the Fermi level, N{sup 2}(E{sub F}). - Graphical abstract: Rate of the nuclear spin-lattice relaxation, 1/T{sub 1}, observed in the {sup 69}Ga NQR experiments for the intermetallic solid solution Fe{sub 1-x}Co{sub x}Ga{sub 3} is the highest for x=0.25 with the highest calculated density of electronic states at the Fermi level, N(E{sub F}); in general, 1/T{sub 1} correlates with N{sup 2}(E{sub F}). Highlights: Black-Right-Pointing-Pointer Fe{sub 1-x}Co{sub x}Ga{sub 3} solid solution is prepared in single crystalline form from Ga flux. Black-Right-Pointing-Pointer In the crystal structure Fe-Fe and Co-Co dumbbells are preferred to Fe-Co dumbbells. Black-Right-Pointing-Pointer Metal-to-semiconductor transition occurs at 0
Calculation and Analysis of Valence Electron Structure of Mo2C and V4C3 in Hot Working Die Steel
Institute of Scientific and Technical Information of China (English)
LIU Yan; LIU Zhi-lin; ZHANG Cheng-wei
2006-01-01
Taking the hot working die steel (HWDS) 4Cr3Mo2NbVNi as an example, the phase electron structures (PES) and the biphase interface electron structures (BIES) of Mo2C and V4C3, which are two kinds of important carbides precipitated during tempering in steel were calculated, on the basis of the empirical electron theory of solids and molecules and the improved TFD theory. The influence of Mo2C and V4C3 on the mechanical properties of HWDS has been analyzed at electron structure level, and the fundamental reason that the characteristic of the PES and the BIES of carbides decides the behavior of them has been revealed.
Powell, B J; Bernstein, N; Brake, K; McKenzie, Ross H; Meredith, P; Pederson, M R
2016-01-01
We report first principles density functional calculations for hydroquinone (HQ), indolequinone (IQ) and semiquinone (SQ). These molecules are believed to be the basic building blocks of the eumelanins, a class of bio-macromolecules with important biological functions (including photoprotection) and with potential for certain bioengineering applications. We have used the DeltaSCF (difference of self consistent fields) method to study the energy gap between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO), Delta_HL. We show that Delta_HL is similar in IQ and SQ but approximately twice as large in HQ. This may have important implications for our understanding of the observed broad band optical absorption of the eumelanins. The possibility of using this difference in Delta_HL to molecularly engineer the electronic properties of eumelanins is discussed. We calculate the infrared and Raman spectra of the three redox forms from first principles. Each of the molecules ...
Singh, Swapnil; Singh, Harshita; Srivastava, Anubha; Tandon, Poonam; Sinha, Kirti; Bharti, Purnima; Kumar, Sudhir; Kumar, Padam; Maurya, Rakesh
2014-11-11
In the present work, a detailed conformational study of cladrin (3-(3,4-dimethoxy phenyl)-7-hydroxychromen-4-one) has been done by using spectroscopic techniques (FT-IR/FT-Raman/UV-Vis/NMR) and quantum chemical calculations. The optimized geometry, wavenumber and intensity of the vibrational bands of the cladrin in ground state were calculated by density functional theory (DFT) employing 6-311++G(d,p) basis sets. The study has been focused on the two most stable conformers that are selected after the full geometry optimization of the molecule. A detailed assignment of the FT-IR and FT-Raman spectra has been done for both the conformers along with potential energy distribution for each vibrational mode. The observed and scaled wavenumber of most of the bands has been found to be in good agreement. The UV-Vis spectrum has been recorded and compared with calculated spectrum. In addition, 1H and 13C nuclear magnetic resonance spectra have been also recorded and compared with the calculated data that shows the inter or intramolecular hydrogen bonding. The electronic properties such as HOMO-LUMO energies were calculated by using time-dependent density functional theory. Molecular electrostatic potential has been plotted to elucidate the reactive part of the molecule. Natural bond orbital analysis was performed to investigate the molecular stability. Non linear optical property of the molecule have been studied by calculating the electric dipole moment (μ) and the first hyperpolarizability (β) that results in the nonlinearity of the molecule.
Tatemizo, N.; Imada, S.; Miura, Y.; Yamane, H.; Tanaka, K.
2017-03-01
The valence band (VB) structures of wurtzite AlCrN (Cr concentration: 0-17.1%), which show optical absorption in the ultraviolet-visible-infrared light region, were investigated via photoelectron yield spectroscopy (PYS), x-ray/ultraviolet photoelectron spectroscopy (XPS/UPS), and ab initio density of states (DOS) calculations. An obvious photoelectron emission threshold was observed ~5.3 eV from the vacuum level for AlCrN, whereas no emission was observed for AlN in the PYS spectra. Comparisons of XPS and UPS VB spectra and the calculated DOS imply that Cr 3d states are formed both at the top of the VB and in the AlN gap. These data suggest that Cr doping could be a viable option to produce new materials with relevant energy band structures for solar photoelectric conversion.
Bates, Kevin R.; Daniels, Andrew D.; Scuseria, Gustavo E.
1998-01-01
We report a comparison of two linear-scaling methods which avoid the diagonalization bottleneck of traditional electronic structure algorithms. The Chebyshev expansion method (CEM) is implemented for carbon tight-binding calculations of large systems and its memory and timing requirements compared to those of our previously implemented conjugate gradient density matrix search (CG-DMS). Benchmark calculations are carried out on icosahedral fullerenes from C60 to C8640 and the linear scaling memory and CPU requirements of the CEM demonstrated. We show that the CPU requisites of the CEM and CG-DMS are similar for calculations with comparable accuracy.
Indian Academy of Sciences (India)
N Boukhris; H Meradji; S Amara Korba; S Drablia; S Ghemid; F El Haj Hassan
2014-08-01
The structural, electronic and thermal properties of lead chalcogenides PbS, PbSe and BeTe using full-potential linear augmented plane wave (FP-LAPW) method are investigated. The exchange–correlation energy within the local density approximation (LDA) and the generalized gradient approximation (GGA) are described. The calculated structural parameters are in reasonable agreement with the available experimental and theoretical data. The electronic band structure shows that the fundamental energy gap is direct (L–L) for all the compounds. Thermal effects on some macroscopic properties of these compounds are predicted using the quasi-harmonic Debye model, in which the lattice vibrations are taken into account. The variations of the lattice constant, bulk modulus, heat capacity, volume expansion coefficient and Debye temperature with temperature and pressure are obtained successfully. The effect of spin–orbit interaction is found to be negligible in determining the thermal properties and leads to a richer electronic structure.
Iwano, Kaoru; Shimoi, Yukihiro
2009-02-01
Density-functional theory (DFT) calculations are performed based on the high-temperature structure of (EDO-TTF)2PF6, a quasi-one-dimensional molecular compound that shows both thermal and photoinduced phase transitions. In this structure, the EDO-TTF molecules are one-dimensionally aligned, accompanied with weak dimerization. Contrary to a common sense, our DFT calculations reveal that the pair having a shorter mutual distance has a weaker intermolecular coupling than the pair with a longer one; the latter is appropriate to be called an electronic dimer. We also estimate the corresponding transfer energies and discuss their relevance to spin correlations and optical excitations.
Energy Technology Data Exchange (ETDEWEB)
Khenata, R.; Baltache, H.; Sahnoun, M.; Driz, M.; Rerat, M.; Abbar, B
2003-08-01
A theoretical study of structural and electronic properties of GeC, SnC and GeSn is presented using the full potential linearized augmented plane wave method. In this approach, the generalized gradient approximation was used for the exchange-correlation potential. Results are given for lattice constant, bulk modulus and its pressure derivative in both zinc-blende and rocksalt structures. Band structure, density of states and band gap pressure coefficients in zinc-blende structure are also given. The results are compared with previous calculations and with experimental measurements.
Brik, M. G.; Avram, N. M.; Gruia, A. S.
2013-08-01
Spectral, structural and electronic properties of two Cr3+-bearing systems (NaCrSi2O6, LiCrSi2O6) have been theoretically modeled using two different approaches: semi-empirical model of crystal field, in the framework of the Exchange Charge Model and two ab initio DFT-based calculations, as implemented in the CASTEP module [1] of Materials Studio package [2] and, for reliability, CRYSTAL09 code [3]. The first one allows for calculations of the electronic levels of sixfold coordinated Cr3+ ions in a crystal field of host's ligands and direct comparison with experimental absorption spectra [4]. The latter two allow for the analysis of the band structure and density of states (DOS), after optimization of the crystal lattice structures of these materials. In particular, a special attention was paid to the energetic position of the Cr3+ 3d states. All obtained results are compared with corresponding experimental values and discussed.
First-principles calculations of structural, electronic and optical properties of CdxZn1-xS alloys
Noor, Naveed Ahmed
2010-10-01
Structural, electronic and optical properties of ternary alloy system CdxZn1-xS have been studied using first-principles approach based on density functional theory. Electronic structure, density of states and energy band gap values for CdxZn1-xS are estimated in the range 0 ≤ x ≤ 1 using both the standard local density approximation (LDA) as well as the generalized gradient approximations (GGA) of Wu-Cohen (WC) for the exchange-correlation potential. It is observed that the direct band gap EgΓ-Γ of CdxZn1-xS decreases nonlinearly with the compositional parameter x, as observed experimentally. It is also found that Cd s and d, S p and Zn d states play a major role in determining the electronic properties of this alloy system. Furthermore, results for complex dielectric constant ε(ω), refractive index n(ω), normal-incidence reflectivity R(ω), absorption coefficient α(ω) and optical conductivity σ(ω) are also described in a wide range of the incident photon energy and compared with the existing experimental data. © 2010 Elsevier B.V. All rights reserved.
Energy Technology Data Exchange (ETDEWEB)
Sheu, Hong-Li; Boopalachandran, Praveenkumar [Department of Chemistry, Texas A& M University, College Station, TX 77843-3255 (United States); Kim, Sunghwan [National Center for Biotechnology Information, National Library of Medicine, National Institutes of Health, Department of Health and Human Services, 8600 Rockville Pike, Bethesda, MD 20894 (United States); Laane, Jaan, E-mail: laane@chem.tamu.edu [Department of Chemistry, Texas A& M University, College Station, TX 77843-3255 (United States)
2015-07-29
Highlights: • The structures of 2,3,5,6-tetrafluoropyridine for its S{sub 0} and S{sub 1}(π, π{sup ∗}) states have been calculated. • TFPy is rigidly planar in its ground electronic state, but is quasi-planar and floppy in S{sub 1}. • The barrier to planarity is 30 cm{sup −1} in the excited state. • The observed vibrational frequencies for both states agree well with the computations. • A ring-bending potential energy function for the S{sub 1}(π, π{sup ∗}) state was proposed. - Abstract: Infrared and Raman spectra of 2,3,5,6-tetrafluoropyridine (TFPy) were recorded and vibrational frequencies were assigned for its S{sub 0} electronic ground states. Ab initio and density functional theory (DFT) calculations were used to complement the experimental work. The lowest electronic excited state of this molecule was investigated with ultraviolet absorption spectroscopy and theoretical CASSCF calculations. The band origin was found to be at 35,704.6 cm{sup −1} in the ultraviolet absorption spectrum. A slightly puckered structure with a barrier to planarity of 30 cm{sup −1} was predicted by CASSCF calculations for the S{sub 1}(π, π{sup ∗}) state. Lower frequencies for the out-of-plane ring bending vibrations for the electronic excited state result from the weaker π bonding within the pyridine ring.
Electronic structure of BaFe2As2 as obtained from DFT/ASW first-principles calculations
Schwingenschlögl, Udo
2010-07-02
We use ab-initio calculations based on the augmented spherical wave method within density functional theory to study the magnetic ordering and Fermi surface of BaFe2As2, the parent compound of the hole-doped iron pnictide superconductors (K,Ba)Fe2As2, for the tetragonal I4/mmm as well as the orthorhombic Fmmm structure. In comparison to full potential linear augmented plane wave calculations, we obtain significantly smaller magnetic energies. This finding is remarkable, since the augmented spherical wave method, in general, is known for a most reliable description of magnetism. © 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Middleton, Kirsten; Zhang, Guoping; George, Thomas F.
2012-02-01
Memantine is currently used as a treatment for mild to severe Alzheimer's disease, although its functionality is complicated. Using various density functional theory calculations and basis sets, we first examine memantine alone and then add ions which are present in the human body. This provides clues as to how the compound may react in the calcium ion channel, where it is believed to treat the disease. In order to understand the difference between calcium and magnesium ions interacting with memantine, we compute the electron affinity of each complex. We find that memantine is more strongly attracted to magnesium ions than calcium ions within the channel. By observing the HOMO-LUMO gap within memantine in comparison to adamantane, we find that memantine is more excitable than the anti-flu drug. We believe these factors to affect the efficiency of memantine as a treatment of Alzheimer's disease.
Directory of Open Access Journals (Sweden)
Alexander L. Ivanovskii
2008-01-01
Full Text Available Atomic models of cubic crystals (CC of carbon and graphene-like Si nanotubes are offered and their structural, cohesive, elastic and electronic properties are predicted by means of the DFTB method. Our main findings are that the isotropic crystals of carbon nanotubes adopt a very high elastic modulus B and low compressibility β, namely B = 650 GPa, β = 0.0015 1/GPa. In addition, these crystals preserve the initial conductivity type of their “building blocks”, i.e. isolated carbon and Si nanotubes. This feature may be important for design of materials with the selected conductivity type.
Energy Technology Data Exchange (ETDEWEB)
Benkabou, M. [Laboratoire des Matériaux Magnétiques, Faculté des Sciences, Université DjillaliLiabès de Sidi Bel-Abbès, Sidi Bel-Abbès 22000 (Algeria); Rached, H. [Laboratoire des Matériaux Magnétiques, Faculté des Sciences, Université DjillaliLiabès de Sidi Bel-Abbès, Sidi Bel-Abbès 22000 (Algeria); Département de Physique, Faculté des Sciences, Université Hassiba Benbouali, Chlef 02000 (Algeria); Abdellaoui, A. [Laboratoire des Matériaux Magnétiques, Faculté des Sciences, Université DjillaliLiabès de Sidi Bel-Abbès, Sidi Bel-Abbès 22000 (Algeria); Rached, D., E-mail: rachdj@yahoo.fr [Laboratoire des Matériaux Magnétiques, Faculté des Sciences, Université DjillaliLiabès de Sidi Bel-Abbès, Sidi Bel-Abbès 22000 (Algeria); Khenata, R. [Laboratoire de Physique Quantique et de Modélisation Mathématique de la Matière, (LPQ3M), Université de Mascara, Mascara 29000 (Algeria); and others
2015-10-25
First-principle calculations are performed to predict the electronic structure and elastic and magnetic properties of CoRhMnZ (Z = Al, Ga, Ge and Si) Heusler alloys. The calculations employ the full-potential linearized augmented plane wave. The exchange-correlations are treated within the generalized gradient approximation of Perdew–Burke and Ernzerhof (GGA-PBE). The electronic structure calculations show that these compounds exhibit a gap in the minority states band and are clearly half-metallic ferromagnets, with the exception of the CoRhMnAl and CoRhMnGa, which are simple ferromagnets that are nearly half metallic in nature. The CoRhMnGe and CoRhMnSi compounds and their magnetic moments are in reasonable agreement with the Slater-Pauling rule, which indicates the half metallicity and high spin polarization for these compounds. At the pressure transitions, these compounds undergo a structural phase transition from the Y-type I → Y-type II phase. We have determined the elastic constants C{sub 11}, C{sub 12} and C{sub 44} and their pressure dependence, which have not previously been established experimentally or theoretically. - Highlights: • Based on DFT calculations, CoRhMnZ (Z = Al, Ga, Ge and Si) Heusler alloys were investigated. • The magnetic phase stability was determined from the total energy calculations. • The mechanical properties were investigated.
Li, Zongbao; Wang, Xia; Xing, Xiaobo; Wang, Ying
2017-02-01
Using density functional theory, we calculated the geometries, band structures and densities of states of W-doped, N-doped, and W/N-codoped anatase TiO4 (001) and (101) surfaces, as well as while the formation energies, based on the overall reaction energy diagram. The calculated results reveal that, on the two surfaces, the absorption of W atoms are more stable than that of N atoms while a larger energy barrier blocks the transfer of W atoms from the surfaces to the body. For TiO2(001), the W-doping and the N/W-codoping lead to a visible lattice distortion while the recombination of photo-generated electron-holes pairs is reduced. A comprehensive analysis of the electronic structures show that the band-gap narrows and a new W-N bond appears, which obviously enhance the photocatalytic activity.
Energy Technology Data Exchange (ETDEWEB)
Matar, Samir F. [CNRS, ICMCB, UPR 9048, Pessac (France); Bordeaux Univ., Pessac (France). ICMCB, UPR 9048; Al Alam, Adel F.; Ouaini, Naim [Univ. Saint Esprit de Kaslik (USEK), Jounieh (Lebanon). URA GREVE, CSR-USEK
2013-01-15
For equiatomic MgNi which can be hydrogenated up to the composition MgNiH{sub 1.6} at an absorption/desorption temperature of 200 C, the effects of hydrogen absorption are approached with the model structures MgNiH, MgNiH{sub 2} and MgNiH{sub 3}. From full geometry optimization and calculated cohesive energies obtained within DFT, the MgNiH{sub 2} composition close to the experimental limit is identified as most stable. Charge density analysis shows an increasingly covalent character of hydrogen: MgNiH(H{sup -0.67}) {yields} MgNiH{sub 2}(H{sup -0.63}) {yields} MgNiH{sub 3}(H{sup -0.55}). While Mg-Ni bonding prevails in MgNi and hydrogenated model phases, extra itinerant low-energy Ni states appear when hydrogen is introduced signaling Ni-H bonding which prevails over Mg-H as evidenced from total energy calculations and chemical bonding analyses. (orig.)
Fatma, Shaheen; Bishnoi, Abha; Singh, Vineeta; Al-Omary, Fatmah A. M.; El-Emam, Ali A.; Pathak, Shilendra; Srivastava, Ruchi; Prasad, Onkar; Sinha, Leena
2016-04-01
Quantum chemical calculations of geometrical structure, energy and vibrational wavenumbers of a novel functionalized pyrido-pyrimidine compound (a prospective antibacterial agent), chemically known as 6-Methyl,13,14,15-Trihydro-14-(4-Nitrophenyl)pyrido[1,2-a:1‧,2‧-a‧] pyrido[2″,3″-d:6″,5″-d‧]dipyrimidine-13,15-dione (C24H16N6O4), were carried out, using B3LYP/6311++G(d,p) method. Comprehensive interpretation of the infrared and Raman spectra of the compound under study is based on potential energy distribution. A good coherence between experimental and theoretical wavenumbers shows the preciseness of the assignments. NLO properties like the dipole moment, polarizability, first static hyperpolarizability and molecular electrostatic potential surface have been calculated to get a better cognizance of the properties of the title compound. Molecular docking results reveal that the title compound exhibit inhibitory activity against Staphylococcus aureus.
Mizutani, U.; Asahi, R.; Sato, H.; Noritake, T.; Takeuchi, T.
2008-07-01
The first-principles FLAPW (full potential linearized augmented plane wave) electronic structure calculations were performed for the Ag5Li8 gamma-brass, which contains 52 atoms in a unit cell and has been known for many years as one of the most structurally complex alloy phases. The calculations were also made for its neighboring phase AgLi B2 compound. The main objective in the present work is to examine if the Ag5Li8 gamma-brass is stabilized at the particular electrons per atom ratio e/a = 21/13 in the same way as some other gamma-brasses like Cu5Zn8 and Cu9Al4, obeying the Hume-Rothery electron concentration rule. For this purpose, the e/a value for the Ag5Li8 gamma-brass as well as the AgLi B2 compound was first determined by means of the FLAPW-Fourier method we have developed. It proved that both the gamma-brass and the B2 compound possess an e/a value equal to unity instead of 21/13. Moreover, we could demonstrate why the Hume-Rothery stabilization mechanism fails for the Ag5Li8 gamma-brass and proposed a new stability mechanism, in which the unique gamma-brass structure can effectively lower the band-structure energy by forming heavily populated bonding states near the bottom of the Ag-4d band.
Medeiros, Subenia; Araujo, Maeva
2015-03-01
The structural, electronic, vibrational, and optical properties of perovskite CaTiO3 in the cubic, orthorhombic, and tetragonal phase are calculated in the framework of density functional theory (DFT) with different exchange-correlation potentials by CASTEP package. The calculated band structure shows an indirect band gap of 1.88 eV at the Γ-R points in the Brillouin zone to the cubic structure, a direct band gap of 2.41 eV at the Γ- Γ points to the orthorhombic structure, and an indirect band gap of 2.31 eV at theM - Γ points to the tetragonal phase. It is still known that the CaTiO3 has a static dielectric constant that extrapolates to a value greater than 300 at zero temperature, and the dielectric response is dominated by low frequency (ν ~ 90cm-1) polar optical modes in which cation motion opposes oxygen motion. Our calculated lattice parameters, elastic constants, optical properties, and vibrational frequencies are found to be in good agreement with the available theoretical and experimental values. The results for the effective mass in the electron and hole carriers are also presented in this work.
Errandonea, D.; Segura, A.; Manjón, F. J.; Chevy, A.; Machado, E.; Tobias, G.; Ordejón, P.; Canadell, E.
2005-03-01
This paper reports on Hall effect and resistivity measurements under high pressure up to 3-4 GPa in p -type γ -indium selenide (InSe) (doped with As, Cd, or Zn) and ɛ -gallium selenide (GaSe) (doped with N or Sn). The pressure behavior of the hole concentration and mobility exhibits dramatic differences between the two layered compounds. While the hole concentration and mobility increase moderately and monotonously in ɛ -GaSe, a large increase of the hole concentration near 0.8 GPa and a large continuous increase of the hole mobility, which doubled its ambient pressure value by 3.2 GPa, is observed in γ -InSe. Electronic structure calculations show that the different pressure behavior of hole transport parameters can be accounted for by the evolution of the valence-band maximum in each material under compression. While the shape of the valence band maximum is virtually pressure-insensitive in ɛ -GaSe, it changes dramatically in γ -InSe, with the emergence of a ring-shaped subsidiary maximum that becomes the absolute valence-band maximum as pressure increases. These differences are shown to be a consequence of the presence or absence of a symmetry element (mirror plane perpendicular to the anisotropy axis) in the point group of each polytype ( D3h for the ɛ -polytype and C3v for the γ -polytype), resulting in different selection rules that affect the k⃗•p⃗ interaction between valence bands.
Harb, Moussab
2013-08-29
Density functional theory (DFT) and density functional perturbation theory (DFPT) were applied to study the structural, electronic, and optical properties of a (Na2-xCux)Ta4O11 solid solution to accurately calculate the band gap and to predict the optical transitions in these materials using the screened coulomb hybrid (HSE06) exchange-correlation formalism. The calculated density of states showed excellent agreement with UV-vis diffuse reflectance spectra predicting a significant red-shift of the band gap from 4.58 eV (calculated 4.94 eV) to 2.76 eV (calculated 2.60 eV) as copper content increased from 0 to 83.3%. The band gap narrowing in these materials, compared to Na2Ta4O11, results from the incorporation of new occupied electronic states, which are strongly localized on the Cu 3d orbitals, and is located within 2.16-2.34 eV just above the valence band of Na2Ta4O11. These new occupied states, however, possess an electronic character localized on Cu, which makes hole mobility limited in the semiconductor. © 2013 American Chemical Society.
Energy Technology Data Exchange (ETDEWEB)
Ciftci, Yasemin Oe. [Gazi Univ., Ankara (Turkey). Dept. of Physics; Coban, Cansu [Balikesir Univ. (Turkey). Dept. of Physics
2016-05-01
The structural, mechanical, electronic, dynamic, and optical properties of the ZrPdSn compound crystallising into the MgAgAs structure are investigated by the ab initio calculations based on the density functional theory. The lattice constant, bulk modulus, and first derivative of bulk modulus were obtained by fitting the calculated total energy-atomic volume results to the Murnaghan equation of state. These results were compared to the previous data. The band structure and corresponding density of states (DOS) were also calculated and discussed. The elastic properties were calculated by using the stress-strain method, which shows that the MgAgAs phase of this compound is mechanically stable. The presented phonon dispersion curves and one-phonon DOS confirms that this compound is dynamically stable. In addition, the heat capacity, entropy, and free energy of ZrPdSn were calculated by using the phonon frequencies. Finally, the optical properties, such as dielectric function, reflectivity function, extinction coefficient, refractive index, and energy loss spectrum, were obtained under different pressures.
Institute of Scientific and Technical Information of China (English)
无
2009-01-01
In this work,the relationship between electronic structure and hemocompatibility of oxygen deficient rutile TiO2-x was studied by both theoretical calculation and experimental study. Based on the local density functional theory,first-principals method was performed to calculate the electronic structure of rutile TiO2 with different oxygen vacancy concentration. In the range of less than 10% of (or equal) physically realistic O vacancy concentration,the band gap of rutile TiO2 increases with increasing O vacancy concentration,leading the TiO2 changes from a p-type to an n-type semiconductor. The valance band of TiO2 is predominated by O 2p orbital,while the conduction band is occupied by Ti 3d orbital for different O vacancy concentration. The O vacancy results in the occupation of electrons at the bottom of conduction band of TiO2,and the donor density increases with increasing O vacancy concentration. When materials come in contact with blood,the n-type semiconductor feature of oxygen deficient TiO2-x with the bottom of conduction band occupied by electrons would prevent charge transfer from fibrinogen into the surface of materials,thus inhibiting the aggregation and activation of platelets,therefore improving the hemocompatibility of rutile TiO2-x.
Institute of Scientific and Technical Information of China (English)
WANG Dajun; XIA Shangda; YIN Min
2008-01-01
The ab initio self-consistent DV-Xα (discrete variational Xα) method was used in its relativistic and spin-polarized model to investigate the ground-state electronic structures of the crystal YPO4 and YPO4:RE3+ (RE=Ce, Pr and Sm) and f-d transition energies of the lattice. The calculation was performed on the clusters Y5P10O32 and REY4P10O32 embedded in a microcrystal containing about 1500 ions, respectively. The ground-state calculation provided the locations of the 4f and 5d crystal-field one-electron levels of RE3+ relative to the valence and conduction bands of host, the curve of total and the partial density of states, and the corresponding occupation numbers, etc. Especially, the transition-state calculation was performed to obtain the 4f→5d transition energies of RE3+ in comparison to the experimental observations. The lattice relaxation caused by the dopant ion RE3+ was discussed based on the total energy calculation and the transition-state calculation of the f-d transition energies.
Energy Technology Data Exchange (ETDEWEB)
Liu, Qi-Jun, E-mail: qijunliu@home.swjtu.edu.cn [Bond and Band Engineering Group, Institute of High Temperature and High Pressure Physics, School of Physical Science and Technology, Southwest Jiaotong University, Chengdu, Sichuan 610031 (China); Zhang, Ning-Chao; Liu, Fu-Sheng [Bond and Band Engineering Group, Institute of High Temperature and High Pressure Physics, School of Physical Science and Technology, Southwest Jiaotong University, Chengdu, Sichuan 610031 (China); Liu, Zheng-Tang [State Key Laboratory of Solidification Processing, School of Materials Science and Engineering, Northwestern Polytechnical University, Xi’an, Shaanxi 710072 (China)
2014-03-15
Highlights: • OsTM and TMOs{sub 2} compounds have no superhard character. • These compounds are mechanically stable and behave in ductile manner. • OsTM has a mixture of covalent-ionic and metallic character. -- Abstract: The first-principles calculations have been performed to study the structural, elastic, mechanical and electronic properties of cubic OsTM (TM = Ti, Zr, and Hf) and hexagonal TMOs{sub 2} compounds. The calculated structural parameters are in good agreement with the available experimental data. To the best of our knowledge, the elastic constants of OsTM and TMOs{sub 2} compounds have been obtained for the first time. The calculated elastic and mechanical properties show that these compounds have no superhard character. These compounds are mechanically stable and behave in ductile manner. The electronic band structures and densities of states of OsTM and TMOs{sub 2} compounds have been analysed. OsTM has a mixture of covalent-ionic and metallic character, and TMOs{sub 2} has strong metallic nature.
Long, Run
2013-04-18
The electronic structure of the TiO2(110) surface interfaced with both a semiconducting and metallic carbon nanotube (CNT) was investigated by density functional theory. Our simulations rationalized visible light photocatalytic activity of CNT/TiO2 hybrid materials higher than that under ultraviolent irradiation and showed that the photoactivity of a semiconducting CNT decorating TiO2 is better than that of the metallic CNT/TiO2 system due to efficient charge separation across the interface. This suggests that semiconducting CNT/TiO2 could be a potential photovoltaic material. In contrast, strong interaction between a metallic CNT and TiO2 leads to large charge transfer. Such charge transfer reduces the built-in potential, in turn resulting in inefficient charge separation. Functionalizing the metallic CNT with a small platinum cluster can increase the built-in potential and drive charge separation. These observations indicate that the CNT/TiO2 interface can be a potential photovoltaic material by a metal cluster decorating a CNT despite a real tube being composed of the mixture of metallic and semiconducting CNTs.
Energy Technology Data Exchange (ETDEWEB)
Lambrecht, Daniel S.; McCaslin, Laura; Xantheas, Sotiris S.; Epifanovsky, Evgeny; Head-Gordon, Martin
2012-09-06
This work reports refinements of the energetic ordering of the known low-energy structures of sulfate-water clusters SO_{4}^{2-} (H2O)n (n = 3-6) using high-level electronic structure methods. Coupled cluster singles and doubles with perturbative triples (CCSD(T)) is used in combination with an estimate of basis set effects up to the complete basis set limit using second order Møller-Plesset theory. Harmonic zero point energy (ZPE), included at the B3LYP/6-311++G** level, was found to have a significant effect on the energetic ordering. Limitations of the ZPE calculations, both due to electronic structure errors, and use of the harmonic approximation, probably constitute the largest remaining errors. Due to the often small energy differences between cluster isomers, and the significant role of ZPE, deuteration can alter the relative energies of low-lying structures, and, when it is applied in conjunction with calculated harmonic ZPE’s, even alters the global minimum for n = 4.
Kabita, Kh; Maibam, Jameson; Indrajit Sharma, B.; Brojen Singh, R. K.; Thapa, R. K.
2016-01-01
We report first principles phase transition, elastic properties and electronic structure for cadmium telluride (CdTe) under induced pressure in the light of density functional theory using the local density approximation (LDA), generalised gradient approximation (GGA) and modified Becke-Johnson (mBJ) potential. The structural phase transition of CdTe from a zinc blende (ZB) to a rock salt (RS) structure within the LDA calculation is 2.2 GPa while that within GGA is found to be at 4 GPa pressure with a volume collapse of 20.9%. The elastic constants and parameters (Zener anisotropy factor, Shear modulus, Poisson’s ratio, Young’s modulus, Kleinmann parameter and Debye’s temperature) of CdTe at different pressures of both the phases have been calculated. The band diagram of the CdTe ZB structure shows a direct band gap of 1.46 eV as predicted by mBJ calculation which gives better results in close agreement with experimental results as compared to LDA and GGA. An increase in the band gap of the CdTe ZB phase is predicted under induced pressure while the metallic nature is retained in the CdTe RS phase.
Mann, Jennifer E; Waller, Sarah E; Jarrold, Caroline Chick
2012-07-28
The anion photoelectron spectra of WAlO(y)(-) (y = 2-4) are presented and assigned based on results of density functional theory calculations. The WAlO(2)(-) and WAlO(3)(-) spectra are both broad, with partially resolved vibrational structure. In contrast, the WAlO(4)(-) spectrum features well-resolved vibrational structure with contributions from three modes. There is reasonable agreement between experiment and theory for all oxides, and calculations are in particular validated by the near perfect agreement between the WAlO(4)(-) photoelectron spectrum and a Franck-Condon simulation based on computationally determined spectroscopic parameters. The structures determined from this study suggest strong preferential W-O bond formation, and ionic bonding between Al(+) and WO(y)(-2) for all anions. Neutral species are similarly ionic, with WAlO(2) and WAlO(3) having electronic structure that suggests Al(+) ionically bound to WO(y)(-) and WAlO(4) being described as Al(+2) ionically bound to WO(4)(-2). The doubly-occupied 3sp hybrid orbital localized on the Al center is energetically situated between the bonding O-local molecular orbitals and the anti- or non-bonding W-local molecular orbitals. The structures determined in this study are very similar to structures recently determined for the analogous MoAlO(y)(-)/MoAlO(y) cluster series, with subtle differences found in the electronic structures [S. E. Waller, J. E. Mann, E. Hossain, M. Troyer, and C. C. Jarrold, J. Chem. Phys. 137, 024302 (2012)].
Dridi, Z; Ruterana, P; Aourag, H
2002-01-01
First-principles calculations have been used to study the effect of vacancies on the structural and electronic properties in substoichiometric TiC sub x and TiN sub x. The effect of vacancies on equilibrium volumes, bulk moduli, electronic band structures and density of states of the substoichiometric phases was studied using a full-potential linear augmented plane-wave method. A model structure of eight-atom supercells with ordered vacancies within the carbon and nitrogen sublattices is used. We find that the lattice parameters of the studied stoichiometries in both TiC sub x and TiN sub x are smaller than that of ideal stoichiometric TiC and TiN. Our results for the variation of the lattice parameters and the bulk moduli for TiC sub x are found to be in good agreement with experiment. The variation of the energy gaps with the atomic concentration ratio shows that these compounds present the same trends. Results for TiC sub x are compared to a recent full-potential calculation with relaxed 16-atom supercells...
Jiang, Hong
2011-05-28
Early transition metal dichalcogenides (TMDC), characterized by their quasi-two-dimensional layered structure, have attracted intensive interest due to their versatile chemical and physical properties, but a comprehensive understanding of their structural and electronic properties from a first-principles point of view is still lacking. In this work, four simple TMDC materials, MX(2) (M = Zr and Hf, X = S and Se), are investigated by the Kohn-Sham density functional theory (KS-DFT) with different local or semilocal exchange-correlation (xc) functionals and many-body perturbation theory in the GW approximation. Although the widely used Perdew-Burke-Ernzelhof (PBE) generalized gradient approximation (GGA) xc functional overestimates the interlayer distance dramatically, two newly developed GGA functionals, PBE-for-solids (PBEsol) and Wu-Cohen 2006 (WC06), can reproduce experimental crystal structures of these TMDC materials very well. The GW method, currently the most accurate first-principles approach for electronic band structures of extended systems, gives the fundamental band gaps of all these materials in good agreement with the experimental values obtained from optical absorption. The minimal direct gaps from GW are systematically larger than those measured from thermoreflectance by about 0.1-0.3 eV, implying that excitonic effects may be stronger than previously estimated. The calculated density of states from GW quasi-particle band energies agrees very well with photo-emission spectroscopy data. Ionization potentials of these materials are also computed by combining PBE calculations based on the slab model and GW quasi-particle corrections. The calculated absolute band energies with respect to the vacuum level indicate that that ZrS(2) and HfS(2), although having suitable band gaps for visible light absorption, cannot be used for overall water splitting as a result of mismatch of the conduction band minimum with the redox potential of H(+)/H(2).
Energy Technology Data Exchange (ETDEWEB)
Piskunov, S. [Institute of Solid State Physics, University of Latvia, Kengaraga 8, LV-1063 Riga (Latvia); Kotomin, E.A. [Institute of Solid State Physics, University of Latvia, Kengaraga 8, LV-1063 Riga (Latvia) and Max-Planck-Institut fuer Festkoerperforschung, Heisenbergstrasse 1, 70569 Stuttgart (Germany)]. E-mail: kotomin@latnet.lv; Fuks, D. [Materials Engineering Department, Ben-Gurion University of the Negev, POB 653, Beer-Sheva (Israel); Dorfman, S. [Department of Physics, Technion- Israel Institute of Technology, Haifa 32000 (Israel)
2005-04-25
Understanding of the atomic and electronic structure of Ba{sub c}Sr{sub 1-c}TiO{sub 3} (BST) solid solutions is important for several applications including the non-volatile ferroelectric memories (dynamic random access memory, DRAM). We present results of ab initio calculations of several spatial arrangements of Ba{sub 0.5}Sr{sub 0.5}TiO{sub 3} solid solutions based on DFT-HF B3PW hybrid method. We calculate the atomic and electronic structure, the effective charges, interatomic bond populations, the electronic density distribution, and densities of states for three layered structures with the same composition. The suggested method reproduces experimental lattice parameters of both pure BaTiO{sub 3} and SrTiO{sub 3}. The calculated optical band gaps for the pure SrTiO{sub 3} and BaTiO{sub 3} are in a good agreement with experimental data, much better than those from the standard LDA or HF calculations. In the studied BST structures with the equiatomic composition (c = 0.5) the gap is reduced by ca. 0.2 eV. The electron density maps demonstrate the covalency effects in the Ti-O bonding. The electron density near the Sr atoms is stronger localized, as compared with the Ba ions.
Directory of Open Access Journals (Sweden)
Niu Mang
2017-01-01
Full Text Available Using density functional theory (DFT, we have investigated the structural and electronic properties of dye-sensitized solar cells (DSSCs comprised of I-doped anatase TiO2(101 surface sensitized with NKX-2554 dye. The calculation results indicate that the cyanoacrylic acid anchoring group in NKX-2554 has a strong binding to the TiO2(101 surface. The dissociative and bidentate bridging type was found to be the most favorable adsorption configuration. On the other hand, the incorporations of I dopant can reduce the band gap of TiO2 photoanode and improve the of NKX-2554 dye, which can improve the visible-light absorption of anatase TiO2 and can also facilitate the electron injection from the dye molecule to the TiO2 substrate. As a result, the I doping can significantly enhance the incident photon-to-current conversion efficiency (IPCE of DSSCs.
Zapata-Rivera, Jhon; Caballol, Rosa; Calzado, Carmen J
2011-04-30
A computational strategy to analyze Cu-O(2) adducts based on the use of difference-dedicated configuration interaction (DDCI) calculations is presented. The electronic structure, vertical gaps and nature of the metal-O(2) interaction, and the extension of the charge transfer between both fragments have been investigated. Relative stabilities between isomers are determined from triplet states CCSD(T) calculations. The key point of the here proposed strategy rests on the use of a rationally designed active space, containing only those orbitals, which optimize the interaction pathways between LCu and O(2) fragments. The procedure has been tested on a broad set of model and synthetic biomimetic systems, the results compared with previous theoretical evaluations and/or available experimental data. Our study indicates that this strategy can be considered as an alternative approach to multireference second-order perturbation theory methods to deal with this type of systems with remarkable biradical nature.
Energy Technology Data Exchange (ETDEWEB)
Pustovarov, V. A. [Ural State Technical University (Russian Federation); Aliev, V. Sh.; Perevalov, T. V., E-mail: timson@isp.nsc.ru; Gritsenko, V. A., E-mail: grits@isp.nsc.ru [Russian Academy of Sciences, Institute of Semiconductor Physics, Siberian Branch (Russian Federation); Eliseev, A. P. [Russian Academy of Sciences, Institute of Geology and Mineralogy, Siberian Branch (Russian Federation)
2010-01-15
The electronic structure of an oxygen vacancy in {alpha}-Al{sub 2}O{sub 3} and {gamma}-Al{sub 2}O{sub 3} is calculated. The calculation predicts an absorption peak at an energy of 6.4 and 6.3 eV in {alpha}-Al{sub 2}O{sub 3} and {gamma}-Al{sub 2}O{sub 3}, respectively. The luminescence and luminescence excitation spectra of amorphous Al{sub 2}O{sub 3} are measured using synchrotron radiation. The presence of a luminescence band at 2.9 eV and a peak at 6.2 eV in the luminescence excitation spectrum indicates the presence of oxygen vacancies in amorphous Al{sub 2}O{sub 3}.
Yang, Kun; He, Yanqing; Cheng, Yi; Che, Li; Yao, Li
2017-03-01
First-principles density functional theory (DFT) calculations have been used to investigate the structural and electronic properties of the cubic KCaF3 and NaCaF3 (001) surfaces with MF (M = K or Na) and CaF2 terminations. For both KCaF3 and NaCaF3 (001) surfaces, the MF termination has stronger surface rumpling than the CaF2 termination. All the computed band gaps for the KCaF3 and NaCaF3 (001) surfaces are smaller than those of the bulks. Furthermore, separated bands that originate from surface layer F p states are introduced at the top of the valance band of MF-terminated surfaces, indicating the emergence of the surface states. The calculated surface energies show that the MF-terminated surface is energetically more favorable than the CaF2-terminated surface.
Energy Technology Data Exchange (ETDEWEB)
Nisikawa, Yunori [Department of Material Science, Osaka City University, Sumiyoshi-ku, Osaka 558-8585 (Japan)]. E-mail: nisikawa@sci.osaka-cu.ac.jp; Usuda, Manabu [Masago 1-4-8, Ibaraki, Osaka, 567-0851 (Japan); Oguri, Akira [Department of Material Science, Osaka City University, Sumiyoshi-ku, Osaka 558-8585 (Japan)
2007-03-15
The electronic structure of CuGeO{sub 3} in the spin-Peierls (SP) phase with the space group of Bbcm is calculated for the first time within the local-density approximation (LDA) and the LDA+U scheme where the local 3d-3d Coulomb interaction U is introduced on the Cu sites. Although the insulating antiferromagnetic solution is obtained in the LDA, the obtained bandgap of 0.19eV and a magnetic moment of 0.39{mu}{sub B}/Cu are much smaller than the experimental bandgap of 3.7eV and the magnetic moment of 0.7{mu}{sub B}/Cu, respectively. With the value of U=6.7eV determined using an electron spectroscopy, the LDA+U calculation yields a charge-transfer bandgap of 1.63eV and gives a magnetic moment of 0.72{mu}{sub B}/Cu. The essential electronic and magnetic properties of CuGeO{sub 3} in the SP phase can be described by means of the LDA+U scheme.
Thanthiriwatte, K Sahan; Wang, Xuefeng; Andrews, Lester; Dixon, David A; Metzger, Jens; Vent-Schmidt, Thomas; Riedel, Sebastian
2014-03-20
Laser-ablated Th atoms react with F2 in condensing noble gases to give ThF4 as the major product. Weaker higher frequency infrared absorptions at 567.2, 564.8 (576.1, 573.8) cm(-1), 575.1 (582.7) cm(-1) and 531.0, (537.4) cm(-1) in solid argon (neon) are assigned to the ThF, ThF2 and ThF3 molecules based on annealing and photolysis behavior and agreement with CCSD(T)/aug-cc-pVTZ vibrational frequency calculations. Bands at 528.4 cm(-1) and 460 cm(-1) with higher fluorine concentrations are assigned to the penta-coordinated species (ThF3)(F2) and ThF5(-). These bands shift to 544.2 and 464 cm(-1) in solid neon. The ThF5 molecule has the (ThF3)(F2) Cs structure and is essentially the unique [ThF3(+)][F2(-)] ion pair based on charge and spin density calculations. Electron capture by (ThF3)(F2) forms the trigonal bipyramidal ThF5(-) anion in a highly exothermic process. Extensive structure and frequency calculations were also done for thorium oxyfluorides and Th2F4,6,8 dimer species. The calculations provide the ionization potentials, electron affinities, fluoride affinities, Th-F bond dissociation energies, and the energies to bind F2 and F2(-) to a cluster as well as dimerization energies.
Lavrentyev, A. A.; Gabrelian, B. V.; Vu, V. T.; Parasyuk, O. V.; Fedorchuk, A. O.; Khyzhun, O. Y.
2016-10-01
A high-quality single crystal of cesium mercury tetrabromide, Cs2HgCl4, was synthesized by using the vertical Bridgman-Stockbarger method and its electronic structure was studied from both experimental and theoretical viewpoints. In particular, X-ray photoelectron spectra were measured for both pristine and Ar+ ion-bombarded Cs2HgCl4 single crystal surfaces. The present XPS measurements indicate that the Cs2HgCl4 single crystal surface is sensitive with respect to Ar+ ion-bombardment: such a treatment changes substantially its elemental stoichiometry. With the aim of exploring total and partial densities of states within the valence band and conduction band regions of the Cs2HgCl4 compound, band-structure calculations based on density functional theory (DFT) using the augmented plane wave + local orbitals (APW + lo) method as incorporated within the WIEN2k package are performed. The calculations indicate that the Cl 3p states are the principal contributors in the upper portion of the valence band, while the Hg 5d and Cs 5p states dominate in its lower portion. In addition, the calculations allow for concluding that the unoccupied Cl p and Hg s states are the main contributors to the bottom of the conduction band. Furthermore, main optical characteristics of Cs2HgCl4, namely dispersion of the absorption coefficient, real and imaginary parts of dielectric function, electron energy-loss spectrum, refractive index, extinction coefficient and optical reflectivity, are elucidated based on the DFT calculations.
Liu, Shuai; Zhan, Yongzhong; Wu, Junyan; Wei, Xuanchen
2015-11-01
The structural, phase stabilities, mechanical, electronic and thermodynamic properties of intermetallic phases in Zr-Sn system are investigated by using first-principles method. The equilibrium lattice constants, enthalpy of formation (ΔHform) and elastic constants are obtained and compared with available experimental and theoretical data. The configuration of Zr4Sn is measured with reasonable precision. The ΔHform of five hypothetical structures are obtained in order to find possible metastable phase for Zr-Sn system. The mechanical properties, including bulk modulus, shear modulus, Young's modulus and Poisson's ratio, are calculated by Voigt-Reuss-Hill approximation and the Zr5Sn4 and Zr5Sn3 show excellent mechanical properties. The electronic density of states for Zr5Sn4, Zr5Sn3 and cP8-Zr3Sn are calculated to further investigate the stability of intermetallic compounds. Through the quasi-harmonic Debye model, the Debye temperature, heat capacity and thermal expansion coefficient under temperature of 0-300 K and pressure of 0-50 GPa for Zr5Sn3 and Zr5Sn4 are deeply investigated.
Ikuhara, Yuichi
2011-01-01
Grain boundaries and interfaces of crystals have peculiar electronic structures, caused by the disorder in periodicity, providing the functional properties, which cannot be observed in a perfect crystal. In the vicinity of the grain boundaries and interfaces, dopants or impurities are often segregated, and they play a crucial role in deciding the properties of a material. Spherical aberration (Cs)-corrected scanning transmission electron microscopy (STEM), allowing the formation of sub-angstrom-sized electron probes, can directly observe grain boundary-segregated dopants. On the other hand, ceramic materials are composed of light elements, and these light elements also play an important role in the properties of ceramic materials. Recently, annular bright-field (ABF)-STEM imaging has been proposed, which is now known to be a very powerful technique in producing images showing both light- and heavy-element columns simultaneously. In this review, the atomic structure determination of ceramic grain boundaries and direct observation of grain boundary-segregated dopants and light elements in ceramics were shown to combine with the theoretical calculations. Examples are demonstrated for well-defined grain boundaries in rare earth-doped Al(2)O(3) and ZnO ceramics, CeO(2) and SrTiO(3) grain boundary, lithium battery materials and metal hydride, which were characterized by Cs-corrected high-angle annular dark-field and ABF-STEM. It is concluded that the combination of STEM characterization and first-principles calculation is very useful in interpreting the structural information and in understanding the origin of the properties in various ceramics.
Energy Technology Data Exchange (ETDEWEB)
Lee, Y.S.
1977-11-01
The effects of the 4f shell of electrons and the relativity of valence electrons are compared. The effect of 4f shell (lanthanide contraction) is estimated from the numerical Hartree-Fock (HF) calculations of pseudo-atoms corresponding to Hf, Re, Au, Hg, Tl, Pb and Bi without 4f electrons and with atomic numbers reduced by 14. The relativistic effect estimated from the numerical Dirac-Hartree-Fock (DHF) calculations of those atoms is comparable in the magnitude with that of the 4f shell of electrons. Both are larger for 6s than for 5d or 6p electrons. The various relativistic effects on valence electrons are discussed in detail to determine the proper level of the approximation for the valence electron calculations of systems with heavy elements. An effective core potential system has been developed for heavy atoms in which relativistic effects are included in the effective potentials.
Energy Technology Data Exchange (ETDEWEB)
Mahmoud, Nada T.; Khalifeh, Jamil M. [Physics Department, The University of Jordan, Amman 11942 (Jordan); Mousa, Ahmad A., E-mail: amousa@meu.edu.jo [Middle East University, P.O. Box 383, Amman 11831 (Jordan); Juwhari, Hassan K.; Hamad, Bothina A. [Physics Department, The University of Jordan, Amman 11942 (Jordan)
2013-12-01
Density Functional Theory (DFT) calculations of a series of the nonstoichiometric Fe{sub 2−x}Co{sub x}VSn full Heusler alloy were carried out utilizing the full potential linearized augmented plane wave (FP-LAPW) method to investigate the electronic, energetic, and magnetic structures of the above systems. Unlike many concentration curves, increasing the cobalt concentration had a crucial effect on the spin polarization as it flattened at 100% at x=1.50, 1.75, and 2.00 where the half- metallic behavior was located with negative formation energy. Moreover, the total magnetic moment of the host material is found to increase with increasing Co concentration. Finally, the half metallic compounds found in some structures of this series might be useful in spintronic devices.
Bilić, Ante; Reimers, Jeffrey R; Hush, Noel S
2005-03-01
The adsorption of phenylthiol on the Au(111) surface is modeled using Perdew and Wang density-functional calculations. Both direct molecular physisorption and dissociative chemisorption via S-H bond cleavage are considered as well as dimerization to form disulfides. For the major observed product, the chemisorbed thiol, an extensive potential-energy surface is produced as a function of both the azimuthal orientation of the adsorbate and the linear translation of the adsorbate through the key fcc, hcp, bridge, and top binding sites. Key structures are characterized, the lowest-energy one being a broad minimum of tilted orientation ranging from the bridge structure halfway towards the fcc one. The vertically oriented threefold binding sites, often assumed to dominate molecular electronics measurements, are identified as transition states at low coverage but become favored in dense monolayers. A similar surface is also produced for chemisorption of phenylthiol on Ag(111); this displays significant qualitative differences, consistent with the qualitatively different observed structures for thiol chemisorption on Ag and Au. Full contours of the minimum potential energy as a function of sulfur translation over the crystal face are described, from which the barrier to diffusion is deduced to be 5.8 kcal mol(-1), indicating that the potential-energy surface has low corrugation. The calculated bond lengths, adsorbate charge and spin density, and the density of electronic states all indicate that, at all sulfur locations, the adsorbate can be regarded as a thiyl species that forms a net single covalent bond to the surface of strength 31 kcal mol(-1). No detectable thiolate character is predicted, however, contrary to experimental results for alkyl thiols that indicate up to 20%-30% thiolate involvement. This effect is attributed to the asymptotic-potential error of all modern density functionals that becomes manifest through a 3-4 eV error in the lineup of the adsorbate and
Structural and electronic properties of half-Heusler alloy PdMnBi calculated from first principles
Energy Technology Data Exchange (ETDEWEB)
Huang, Wenchao, E-mail: wc_huang@mail.sitp.ac.cn [National Laboratory for Infrared Physics, Shanghai Institute of Technical Physics, Chinese Academy of Sciences, Shanghai 200083 (China); Wang, Xiaofang, E-mail: wxiaof66@mail.sitp.ac.cn [National Laboratory for Infrared Physics, Shanghai Institute of Technical Physics, Chinese Academy of Sciences, Shanghai 200083 (China); Chen, Xiaoshuang, E-mail: xschen@mail.sitp.ac.cn [National Laboratory for Infrared Physics, Shanghai Institute of Technical Physics, Chinese Academy of Sciences, Shanghai 200083 (China); Lu, Wei [National Laboratory for Infrared Physics, Shanghai Institute of Technical Physics, Chinese Academy of Sciences, Shanghai 200083 (China); Damewood, L.; Fong, C.Y. [Department of Physics, University of California, Davis, CA 95616-8677 (United States)
2014-11-14
The dependence of the electronic and magnetic properties on the atomic arrangements of three different phases (i.e. α, β, and γ phases), of the half-Heusler alloy PdMnBi, is investigated based on spin-polarized density functional theory. For each phase, the optimized lattice constant is determined and the possibility of finding a half-metal is explored. Throughout this study, the bonding features of each phase are not supported by the large electronegativity of Pd given in the public domain. Both α and β phases PdMnBi show half-metallic (HM) properties for a range of lattice constants, and their magnetic moments are consistent with the values given by the modified Slater-Pauling rule. Additionally, the effects of the spin–orbit (S-O) interaction are examined by comparing the relative shifts of the valence bands and the indirect semiconducting gap, with respect to the spin-polarized results. - Highlights: • We studied all different atomic arrangement (α, β, and γ phases) of PdMnBi. • Detailed explanation of electronic properties for three phases has been given. • We did observed half-metallic properties in alpha and beta phase. • The spin-orbital effect is considered and we made a comparison with NiMnSb.
Interaction between LiH molecule and Li atom from state-of-the-art electronic structure calculations
Skomorowski, Wojciech; Korona, Tatiana; Moszyński, Robert; Zuchowski, Piotr S \\; Hutson, Jeremy M
2010-01-01
State-of-the-art ab initio techniques have been applied to compute the potential energy surface for the lithium atom interacting with the lithium hydride molecule in the Born-Oppenheimer approximation. The interaction potential was obtained using a combination of the explicitly correlated unrestricted coupled-cluster method with single, double, and noniterative triple excitations [UCCSD(T)-F12] for the core-core and core-valence correlation and full configuration interaction for the valence-valence correlation. The potential energy surface has a global minimum 8743 cm^{-1} deep if the Li-H bond length is held fixed at the monomer equilibrium distance or 8825 cm^{-1} deep if it is allowed to vary. In order to evaluate the performance of the conventional CCSD(T) approach, calculations were carried out using correlation-consistent polarized valence X-tuple-zeta bases, with X ranging from 2 to 5. The contribution beyond the CCSD(T)-F12 model, obtained from full configuration interaction (FCI) calculations for the...
Rustad, James R.; Dixon, David A.; Felmy, Andrew R.
2000-05-01
Density functional calculations are performed on M 3(OH) 7(H 2O) 62+ and M 3O(OH) 6(H 2O) 6+ clusters for MAl, Cr(III), and Fe(III), allowing determination of the relative acidities of the μ 3-hydroxo and aquo functional groups. Contrary to previous predictions and rationalizations, Fe 3OH and Al 3OH groups have nearly the same intrinsic acidity, while Cr 3OH groups are significantly more acidic. The gas-phase acidity of the Fe 3OH site is in good agreement with the value predicted by the molecular mechanics model previously used to estimate the relative acidities of surface sites on iron oxides. [ J. R. Rustad et al. (1996)Geochim. Cosmochim. Acta 60, 1563]. Acidities of aquo functional groups were also computed for Al and Cr. The AlOH 2 site is more acidic than the Al 3OH site, whereas the Cr 3OH site is more acidic than the CrOH 2 site. These findings predict that the surface charging behavior of chromium oxides/oxyhydroxides should be distinguishable from their Fe, Al counterparts. The calculations also provide insight into why the lepidocrocite/boehmite polymorph is not observed for CrOOH.
Lahiji, Mohammadreza Askaripour; Ziabari, Ali Abdolahzadeh
2016-11-01
The structural, elastic, electronic, and optical properties of undoped and Cu-doped ZnS nanostructured layers have been studied in the zincblende (ZB) phase, by first-principle approach. Density functional theory (DFT) has been employed to calculate the fundamental properties of the layers using full-potential linearized augmented plane-wave (FPLAPW) method. Mechanical analysis revealed that the bulk modulus increases with the increase of Cu content. Cu doping was found to reduce the band gap value of the material. In addition, DOS effective mass of the electrons and heavy holes was evaluated. Adding Cu caused the decrement/increment of transmission/reflectance of nanolayers in the UV-vis region. The substitution by Cu increased the intensity of the peaks, and a slight red shift was observed in the absorption peak. Moreover, the static dielectric constant, and static refractive index increased with Cu content. The optical conductivity also followed a similar trend to that of the dielectric constants. Energy loss function of the modeled compounds was also evaluated. All calculated parameters were compared with the available experimental and other theoretical results.
DEFF Research Database (Denmark)
Bork, Nicolai Christian; Du, Lin; Kjærgaard, Henrik Grum
2014-01-01
Models of atmospheric aerosol formation are dependent on accurate Gibbs free binding energies (ΔG°) of gaseous acids and bases, but for most acid–base pairs, only ab initio data are available. We report a combined experimental and theoretical study of the gaseous molecular complex of dimethylsulf......Models of atmospheric aerosol formation are dependent on accurate Gibbs free binding energies (ΔG°) of gaseous acids and bases, but for most acid–base pairs, only ab initio data are available. We report a combined experimental and theoretical study of the gaseous molecular complex...... of dimethylsulfide (DMS) and HCl. On the basis of infrared spectroscopy and anharmonic local mode calculations, we determine ΔG(295K)° to be between 6.2 and 11.1 kJ mol(–1). We test the performance of MP2 and five often used DFT functionals with respect to this result. M06-2X performs the best, but also the MP2...
The Electronic Structure of Calcium
DEFF Research Database (Denmark)
Jan, J.-P.; Skriver, Hans Lomholt
1981-01-01
The electronic structure of calcium under pressure is re-examined by means of self-consistent energy band calculations based on the local density approximation and using the linear muffin-tin orbitals (LMTO) method with corrections to the atomic sphere approximation included. At zero pressure.......149 Ryd, respectively, relative to the s band, give the best possible agreement. Under increasing pressure the s and p electrons are found to transfer into the d band, and Ca undergoes metal-semimetal-metal electronic transitions. Calculations of the bandstructure and the electronic pressure, including...
Lavrentyev, A. A.; Gabrelian, B. V.; Vu, V. T.; Denysyuk, N. M.; Shkumat, P. N.; Tarasova, A. Y.; Isaenko, L. I.; Khyzhun, O. Y.
2016-03-01
Density functional theory (DFT) calculations are made in order to explore the total and partial densities of states of potassium dilead pentabromide, KPb2Br5, by using the augmented plane wave + local orbitals (APW + lo) method as incorporated in the WIEN2k package. The present calculations reveal that the principle contributors to the valence band of KPb2Br5 are the Pb 6s and Br 4p states contributing predominantly at the bottom and at the top of the band, respectively, while the bottom of the conduction band is formed mainly from contributions of the unoccupied Pb 6p states. The curves of total density of states derived by the present DFT calculations of KPb2Br5 are found to be in agreement with the experimental X-ray photoelectron valence-band spectrum of the compound studied. Comparison on a common energy scale of the X-ray emission bands representing the energy distribution of the valence Br p and K s states and the X-ray photoelectron valence-band spectrum of the KPb2Br5 single crystal indicate that the Br 4p and K 4s states contribute mainly at the top and in the upper portion of the valence band, respectively, being in agreement with data of the present DFT band-structure calculations of this compound. Principal optical characteristics of KPb2Br5, namely dispersion of the absorption coefficient, real and imaginary parts of dielectric function, electron energy-loss spectrum, refractive index, extinction coefficient and optical reflectivity are also studied by the DFT calculations.
Energy Technology Data Exchange (ETDEWEB)
Ivanov, Maxim V.; Perevalov, Timofey V.; Aliev, Vladimir S.; Gritsenko, Vladimir A. [A. V. Rzhanov Institute of Semiconductor Physics SB RAS, Novosibirsk, 630090 (Russian Federation); Kaichev, Vasily V. [Boreskov Institute of Catalysis SB RAS, Novosibirsk, 630090 (Russian Federation)
2011-07-15
Electronic structure of oxygen vacancies in Ta{sub 2}O{sub 5} have been studied theoretically by first-principles calculations and experimentally by x-ray photoelectron spectroscopy. Calculations of {delta}-Ta{sub 2}O{sub 5} were performed using density functional theory within gradient-corrected approximation with the +U approach. Results indicate that the oxygen vacancy causes a defect level in the energy gap at 1.2 eV above the top of the valence band. To produce oxygen vacancies, amorphous films of Ta{sub 2}O{sub 5} were bombarded with Ar{sup +} ions. XPS results indicate that the Ar-ion bombardment leads to the generation of the oxygen vacancies in Ta{sub 2}O{sub 5} that characterize the peak at 2 eV above the valence band. The calculated spectrum of crystalline {delta}-Ta{sub 2}O{sub 5} demonstrates qualitative correspondence with the XPS spectrum of the amorphous Ta{sub 2}O{sub 5} film after Ar-ion bombardment.
Energy Technology Data Exchange (ETDEWEB)
Nazarov, M. [School of Materials and Mineral Resources Engineering, Universiti Sains Malaysia, Engineering Campus, 14300 Nibong Tebal, Pulau Pinang (Malaysia); Institute of Applied Physics, Academiei Street 5, Chisinau MD-2028 (Moldova, Republic of); Brik, M.G., E-mail: brik@fi.tartu.ee [Institute of Physics, University of Tartu, Riia 142, Tartu 51014 (Estonia); Spassky, D. [Institute of Physics, University of Tartu, Riia 142, Tartu 51014 (Estonia); Skobeltsyn Institute of Nuclear Physics, M.V. Lomonosov Moscow State University, 119991 Moscow (Russian Federation); Tsukerblat, B. [Department of Chemistry, Ben-Gurion University of the Negev, Beer-Sheva 84105 (Israel); Nor Nazida, A. [School of Materials and Mineral Resources Engineering, Universiti Sains Malaysia, Engineering Campus, 14300 Nibong Tebal, Pulau Pinang (Malaysia); Faculty of Art and Design, Universiti Teknologi MARA (Perak), Seri Iskandar, 32610 Bandar Baru Seri Iskandar, Perak (Malaysia); Ahmad-Fauzi, M.N. [School of Materials and Mineral Resources Engineering, Universiti Sains Malaysia, Engineering Campus, 14300 Nibong Tebal, Pulau Pinang (Malaysia)
2013-10-05
Highlights: •Persistent phosphor SrAl{sub 2}O{sub 4}:Eu{sup 2+} was synthesized and studied. •Ab initio calculations of its electronic properties were performed. •Lowest position of the Eu 4f states in the band gap was determined. •Position of the Eu 4f states agrees with the charge transfer transition. -- Abstract: A stoichiometric micro-sized powder SrAl{sub 2}O{sub 4}:Eu{sup 2+} was synthesized by traditional solid state reaction at 1250 °C. Low-temperature spectroscopic measurements revealed two luminescence bands at 450 nm and 512 nm; their origin was discussed. Theoretical calculations of the structural and optical properties of SrAl{sub 2}O{sub 4}:Eu{sup 2+} in the framework of the density functional theory (DFT) were carried out; the obtained results were compared with the corresponding experimental data. For the first time, the position of the lowest 4f states of Eu in the host’s band gap was calculated for both available Sr positions to be at about 4.5–5 eV above the top of the valence band. Reliability of this result is confirmed by good agreement with the experimental value of the O(2p)–Eu(4f) charge transfer energy, which is equal to about 4.9 eV.
Jeeva Jasmine, N.; Arunagiri, C.; Subashini, A.; Stanley, N.; Thomas Muthiah, P.
2017-02-01
Theoretical Spectrograms, namely, FT-Raman (3500-50 cm-1) and FT-Infrared (4000-400 cm-1) spectra have been studied for 4-acetamido benzaldehyde (4ABA) and are assigned to different normal modes of the molecule. Vibrational spectral analysis was compared with the experimental and theoretical, FT-IR and FT-Raman spectra. The effect of polarity on the Harmonic vibrational frequencies, intensities, optimized geometrical parameters and several thermodynamic parameters in the ground state have been computed by the B3LYP method using 6-311 + G(d,p) basis set. The results of the optimized molecular structure is presented and compared with the XRD values. The global chemical reactivity relate to some parameters, such as HOMO, LUMO, gap energy (ΔE) and other parameters, including electronegativity (χ) and global hardness (η). The values of the reactivity descriptors indicated that the interaction between 4ABA molecules reduced its reactivity in comparison with the exhibited in gas phase. In addition, the local reactivity has been analyzed through the Fukui function and condensed softness indices.
Local orbitals in electron scattering calculations*
Winstead, Carl L.; McKoy, Vincent
2016-05-01
We examine the use of local orbitals to improve the scaling of calculations that incorporate target polarization in a description of low-energy electron-molecule scattering. After discussing the improved scaling that results, we consider the results of a test calculation that treats scattering from a two-molecule system using both local and delocalized orbitals. Initial results are promising. Contribution to the Topical Issue "Advances in Positron and Electron Scattering", edited by Paulo Limao-Vieira, Gustavo Garcia, E. Krishnakumar, James Sullivan, Hajime Tanuma and Zoran Petrovic.
Calculated Electron Fluxes at Airplane Altitudes
Schaefer, R K; Stanev, T
1993-01-01
A precision measurement of atmospheric electron fluxes has been performed on a Japanese commercial airliner (Enomoto, {\\it et al.}, 1991). We have performed a monte carlo calculation of the cosmic ray secondary electron fluxes expected in this experiment. The monte carlo uses the hadronic portion of our neutrino flux cascade program combined with the electromagnetic cascade portion of the CERN library program GEANT. Our results give good agreement with the data, provided we boost the overall normalization of the primary cosmic ray flux by 12\\% over the normalization used in the neutrino flux calculation.
Indian Academy of Sciences (India)
S Bendaif; A Boumaza; O Nemiri; K Boubendira; H Meradji; S Ghemid; F El Haj Hassan
2015-04-01
First-principle calculations were performed to study the structural, electronic, thermodynamic and thermal properties of ZnSxSe1−x ternary alloys using the full potential-linearized augmented plane wave method (FP-LAPW) within the density functional theory (DFT). In this approach the Wu–Cohen generalized gradient approximation (WC-GGA) and Perdew–Wang local density approximation (LDA) were used for the exchange–correlation potential. For band structure calculations, in addition to WC-GGA approximation, both Engel–Vosko (EV-GGA) generalized gradient approximation and recently proposed modified Becke–Johnson (mBJ) potential approximation have been used. Our investigation on the effect of composition on lattice constant, bulk modulus and band gap for ternary alloys shows a linear dependence on alloy composition with a small deviation. The microscopic origins of the gap bowing were explained using the approach of Zunger and co-workers. Besides, a regular-solution model was used to investigate the thermodynamic stability of the alloys which mainly indicates a phase miscibility gap. Finally, the quasi-harmonic Debye model was applied to see how the thermal properties vary with temperature at different pressures.
Energy Technology Data Exchange (ETDEWEB)
Bronisz, K. [Department of Physics, Adam Mickiewicz University, Umultowska 85, 61-614 Poznan (Poland); Ostafin, M. [Department of Physics, Adam Mickiewicz University, Umultowska 85, 61-614 Poznan (Poland)], E-mail: ostifnqr@amu.edu.pl; Poleshchuk, O. Kh. [Department of Chemistry, Tomsk Pedagogical University, Komsomolskii 75, 634041 Tomsk (Russian Federation); Mielcarek, J. [Faculty of Pharmacy, University of Medical Sciences, Grunwaldzka 6, 60-780 Poznan (Poland); Nogaj, B. [Department of Physics, Adam Mickiewicz University, Umultowska 85, 61-614 Poznan (Poland)
2006-11-08
Selected derivatives of 1,4-benzodiazepine: lorazepam, lormetazepam, oxazepam and temazepam, used as active substances in anxiolytic drugs, have been studied by {sup 35}Cl NQR method in order to find the correlation between electronic structure and biological activity. The {sup 35}Cl NQR resonance frequencies ({nu} {sub Q}) measured at 77 K have been correlated with the following parameters characterising their biological activity: biological half-life period (t {sub 0.5}), affinity to benzodiazepine receptor (IC{sub 50}) and mean dose equivalent. The results of experimental study of some benzodiazepine derivatives by nuclear quadrupole resonance of {sup 35}Cl nuclei are compared with theoretical results based on DFT calculations which were carried out by means of Gaussian'98 W software.
Energy Technology Data Exchange (ETDEWEB)
Greene-Diniz, Gabriel; Greer, J. C. [Tyndall National Institute, Lee Maltings, Prospect Row, Cork (Ireland); Fischetti, M. V. [Department of Materials Science and Engineering, University of Texas at Dallas, 800 West Campbell Road RL10, Richardson, Texas 75080 (United States)
2016-02-07
Several theoretical electronic structure methods are applied to study the relative energies of the minima of the X- and L-conduction-band satellite valleys of In{sub x}Ga{sub 1−x}As with x = 0.53. This III-V semiconductor is a contender as a replacement for silicon in high-performance n-type metal-oxide-semiconductor transistors. The energy of the low-lying valleys relative to the conduction-band edge governs the population of channel carriers as the transistor is brought into inversion, hence determining current drive and switching properties at gate voltages above threshold. The calculations indicate that the position of the L- and X-valley minima are ∼1 eV and ∼1.2 eV, respectively, higher in energy with respect to the conduction-band minimum at the Γ-point.
Energy Technology Data Exchange (ETDEWEB)
Bannikov, V.V.; Shein, I.R. [Institute of Solid State Chemistry, Ural Branch of the Russian Academy of Sciences, 620990 Ekaterinburg (Russian Federation); Ivanovskii, A.L., E-mail: ivanovskii@ihim.uran.ru [Institute of Solid State Chemistry, Ural Branch of the Russian Academy of Sciences, 620990 Ekaterinburg (Russian Federation)
2012-01-15
The structural, elastic, magnetic and electronic properties of the layered tetragonal phase KCo{sub 2}Se{sub 2} have been examined in details by means of the first-principles calculations and analyzed in comparison with the isostructural KFe{sub 2}Se{sub 2} as the parent phase for the newest group of ternary superconducting iron-chalcogenide materials. Our data show that KCo{sub 2}Se{sub 2} should be characterized as a quasi-two-dimensional ferromagnetic metal with highly anisotropic inter-atomic bonding owing to mixed ionic, covalent, and metallic contributions inside [Co{sub 2}Se{sub 2}] blocks, and with ionic bonding between the adjacent [Co{sub 2}Se{sub 2}] blocks and K sheets. This material should behave in a brittle manner, adopt enhanced elastic anisotropy rather in compressibility than in shear, and should show very low hardness.
Energy Technology Data Exchange (ETDEWEB)
Li, Xuechao; Shi, Jianhao; Zhao, Tong [Department of Materials Physics and Chemistry, Kunming University of Science & Technology, Kunming, Yunnan 650093 (China); Wan, Rundong, E-mail: rdwan@kmust.edu.cn [Department of Materials Physics and Chemistry, Kunming University of Science & Technology, Kunming, Yunnan 650093 (China); Leng, Chongyan [Department of Materials Physics and Chemistry, Kunming University of Science & Technology, Kunming, Yunnan 650093 (China); Lei, Ying [Department of Metallurgical Engineering, Anhui University of Technology, Maanshan, Anhui 243002 (China)
2016-06-01
Abstracts: We carry out theoretical studies for both the pristine and boron-nitrogen co-doped (4,3) single-walled carbon nanotubes (SWCNTs). We first acquire the optimized geometries using a pure functional. We then obtain the electronic structures with a relatively accurate hybrid functional. We systematically study four different patterns for doping along different chain directions. Our calculated results reveal that the energy band splits, and many new states appear in the gap after doping. The band gap gradually decreases with the increasing number of dopants, while it begins to expand when the doping concentration is larger. Through projected density of states analyses, we find that the individual atoms make different contribution to the valence states, gap region states, and conduction states. These findings are expected to provide some reliable theoretical supports with the following research on the modification of carbon nanotubes.
Energies of the X- and L-valleys in In0.53Ga0.47As from electronic structure calculations
Greene-Diniz, Gabriel; Fischetti, M. V.; Greer, J. C.
2016-02-01
Several theoretical electronic structure methods are applied to study the relative energies of the minima of the X- and L-conduction-band satellite valleys of InxGa1-xAs with x = 0.53. This III-V semiconductor is a contender as a replacement for silicon in high-performance n-type metal-oxide-semiconductor transistors. The energy of the low-lying valleys relative to the conduction-band edge governs the population of channel carriers as the transistor is brought into inversion, hence determining current drive and switching properties at gate voltages above threshold. The calculations indicate that the position of the L- and X-valley minima are ˜1 eV and ˜1.2 eV, respectively, higher in energy with respect to the conduction-band minimum at the Γ-point.
Bronisz, K.; Ostafin, M.; Poleshchuk, O. Kh.; Mielcarek, J.; Nogaj, B.
2006-11-01
Selected derivatives of 1,4-benzodiazepine: lorazepam, lormetazepam, oxazepam and temazepam, used as active substances in anxiolytic drugs, have been studied by 35Cl NQR method in order to find the correlation between electronic structure and biological activity. The 35Cl NQR resonance frequencies ( νQ) measured at 77 K have been correlated with the following parameters characterising their biological activity: biological half-life period ( t0.5), affinity to benzodiazepine receptor (IC 50) and mean dose equivalent. The results of experimental study of some benzodiazepine derivatives by nuclear quadrupole resonance of 35Cl nuclei are compared with theoretical results based on DFT calculations which were carried out by means of Gaussian'98 W software.
Energy Technology Data Exchange (ETDEWEB)
Moreira, E. [Departamento de Fisica Teorica e Experimental, Universidade Federal do Rio Grande do Norte, 59072-970 Natal-RN (Brazil); Henriques, J.M. [Centro de Educacao e Saude, Universidade Federal de Campina Grande, Campus Cuite, 58175-000 Cuite-PB (Brazil); Azevedo, D.L. [Departamento de Fisica, Universidade Federal do Maranhao, Centro de Ciencias Exatas e Tecnologia, 65085-580 Sao Luis-MA (Brazil); Caetano, E.W.S., E-mail: ewcaetano@gmail.com [Instituto Federal de Educacao, Ciencia e Tecnologia do Ceara, 60040-531 Fortaleza-CE (Brazil); Freire, V.N. [Departamento de Fisica, Universidade Federal do Ceara, Centro de Ciencias, Caixa Postal 6030, Campus do Pici, 60455-760 Fortaleza-CE (Brazil); Albuquerque, E.L. [Departamento de Biofisica e Farmacologia, Universidade Federal do Rio Grande do Norte, 59072-970 Natal-RN (Brazil)
2012-03-15
Neutron diffraction data for Sr{sub x}Ba{sub 1-x}SnO{sub 3} (x=0.0, 0.2, 0.4, 0.6, 0.8 and 1.0) solid solutions were used as inputs to obtain optimized geometries and electronic properties using the density functional theory (DFT) formalism considering both the local density and generalized gradient approximations, LDA and GGA, respectively. The crystal structures and SnO{sub 6} octahedra tilting angles found after total energy minimization agree well with experiment, specially for the GGA data. Elastic constants were also obtained and compared with theoretical and experimental results for cubic BaSnO{sub 3}. While the alloys with cubic unit cell have an indirect band gap, tetragonal and orthorhombic alloys exhibit direct band gaps (exception made to x=1.0). The Kohn-Sham minimum electronic band gap oscillates from 1.52 eV (cubic x=0.0, LDA) to 2.61 eV (orthorhombic x=1.0, LDA), and from 0.74 eV (cubic BaSnO{sub 3}, GGA) to 1.97 eV (orthorhombic SrSnO{sub 3}, GGA). Parabolic interpolation of bands has allowed us to estimate the effective masses for charge carriers, which are shown to be anisotropic and larger for holes. - Graphical Abstract: Highlights: Black-Right-Pointing-Pointer DFT calculations were performed on Sr{sub x}Ba{sub 1-x}SnO{sub 3} solid solutions. Black-Right-Pointing-Pointer Calculated crystal structures agree well with experiment. Black-Right-Pointing-Pointer Alloys have direct or indirect gaps depending on the Sr molar fraction. Black-Right-Pointing-Pointer The Kohn-Sham gap variation from x=0.0 to x=1.0 is close to the experimental value. Black-Right-Pointing-Pointer Carrier effective masses are very anisotropic, specially for holes.
Energy Technology Data Exchange (ETDEWEB)
Bouhemadou, A. [University of Setif, Laboratory for Developing New Materials and Their Characterization, Department of Physics, Faculty of Science, Setif (Algeria)
2009-09-15
Using ab initio calculations, we have studied the structural, electronic and elastic properties of M{sub 2}GeC, with M=Ti, V, Cr, Zr, Nb, Mo, Hf, Ta and W. Geometrical optimizations of the unit cell are in agreement with the available experimental data. The band structures show that all studied materials are electrical conductors. The analysis of the site and momentum projected densities shows that bonding is due to M d-C p and M d-Ge p hybridizations. The elastic constants are calculated using the static finite strain technique. The shear modulus C{sub 44}, which is directly related to the hardness, reaches its maximum when the valence electron concentration is in the range 8.41-8.50. We derived the bulk and shear moduli, Young's moduli and Poisson's ratio for ideal polycrystalline M{sub 2}GeC aggregates. We estimated the Debye temperature of M{sub 2}GeC from the average sound velocity. This is the first quantitative theoretical prediction of the elastic constants of Ti{sub 2}GeC, V{sub 2}GeC, Cr{sub 2}GeC, Zr{sub 2}GeC, Nb{sub 2}GeC, Mo{sub 2}GeC, Hf{sub 2}GeC, Ta{sub 2}GeC and W{sub 2}GeC compounds, and it still awaits experimental confirmation. (orig.)
Energy Technology Data Exchange (ETDEWEB)
Liu, Hong-Xia [Department of Materials Science and Engineering, Lanzhou University of Technology, State Key Laboratory of Advanced Processing and Recycling of Non-ferrous Metals, Lanzhou 730050 (China); Tang, Fu-Ling, E-mail: tfl03@mails.tsinghua.edu.cn [Department of Materials Science and Engineering, Lanzhou University of Technology, State Key Laboratory of Advanced Processing and Recycling of Non-ferrous Metals, Lanzhou 730050 (China); Xue, Hong-Tao; Zhang, Yu [Department of Materials Science and Engineering, Lanzhou University of Technology, State Key Laboratory of Advanced Processing and Recycling of Non-ferrous Metals, Lanzhou 730050 (China); Feng, Yu-Dong [Science and Technology on Surface Engineering Laboratory, Lanzhou Institute of Physics, Lanzhou 730000 (China)
2015-10-01
Graphical abstract: The atomic structure, bonding energy and electronic properties of the perfect WZ-CIS (1 0 0)/MoS{sub 2} (−1 0 0) interface with a lattice mismatch less than 3.5% are studied using the first principles calculation. - Highlights: • The degree of lattice mismatch of WZ-CuInS{sub 2} (1 0 0)/MoS{sub 2} (−1 0 0) is about 3.5%. • The interface bonding energy is −0.65 J/m{sup 2}, the interface has better stability. • On the interface there are some interface states near the Fermi level mainly caused by In-5s and S-3p orbital. • Difference charge density and Bader charges analysis find that the atoms near the interface have strong charge transfer. • A lot of atomic orbital hybridizations appear on the interface enhanced the interface stability and conductivity. - Abstract: Using first-principles plane-wave calculations within density functional theory, we theoretically studied the perfect WZ-CIS (1 0 0)/MoS{sub 2} (−1 0 0) interface, including the atomic structure, bonding energy and electronic properties. After relaxation the atomic positions and the bond lengths change slightly on the interface. The WZ-CIS/MoS{sub 2} interface can exist stably with the interface bonding energy about −0.65 J/m{sup 2}. Via analysis density of states, difference charge density and Bader charges we find that the electrons are largely redistributed on the interface, and there are some interface states near the Fermi level, which are mainly caused by In-5s orbital in the WZ-CIS region and S-3p orbital in the MoS{sub 2} region. On the interface the orbital hybridizations of different interfacial atoms highly enhance the bonding ability of the atoms. Electron transformation and orbital hybridization together promote the bonding between atoms and increase the adhesion energy of the interface.
Program Calculates Current Densities Of Electronic Designs
Cox, Brian
1996-01-01
PDENSITY computer program calculates current densities for use in calculating power densities of electronic designs. Reads parts-list file for given design, file containing current required for each part, and file containing size of each part. For each part in design, program calculates current density in units of milliamperes per square inch. Written by use of AWK utility for Sun4-series computers running SunOS 4.x and IBM PC-series and compatible computers running MS-DOS. Sun version of program (NPO-19588). PC version of program (NPO-19171).
Electronic band structure of a type-Ⅱ 'W' quantum well calculated by an eight-band k·p model
Institute of Scientific and Technical Information of China (English)
Yu Xiu; Gu Yong-Xian; Wang Qing; Wei Xin; Chen Liang-Hui
2011-01-01
In this paper, we present an investigation of type-Ⅱ 'W' quantum wells for the InAs/Ga1-xInxSb/AlSb family, where 'W' denotes the conduction profile of the material. We focus our attention on using the eight-band k·p model to calculate the band structures within the framework of finite element method. For the sake of clarity, the simulation in this paper is simplified and based on only one period-AlSb/InAs/Ga1-xInxSb/InAs/AlSb. The obtained numerical results include the energy levels and wavefunctions of carriers. We discuss the variations of the electronic properties by changing several important parameters, such as the thickness of either InAs or Ga1-xInxSb layer and the alloy composition in Ga1-xInxSb separately. In the last part, in order to compare the eight-band k·p model, we recalculate the conduction bands of the 'W' structure using the one-band k·p model and then discuss the difference between the two results, showing that conduction bands are strongly coupled with valence bands in the narrow band gap structure. The in-plane energy dispersions, which illustrate the suppression of the Auger recombination process, are also obtained.
Institute of Scientific and Technical Information of China (English)
Jiang Ying; Zeng Zhi; Xia Shangda; Yin Min
2005-01-01
The electronic structures of LiYF4:Ce3+ and LiYF4 crystals simulated by an embedded (in a microcrystal containing 1938 ions) cluster CeY4Li8F24, and Y5Li8F24 respectively, were computed by the ab initio self-consistent relativistic DV-Xa(discrete variational Xa) method. The ground-state calculation showed that only the lowest 5d level Ed of Ce3+ ion lies around the BCB (bottom of the conduction band) while the lowest 4f levels is 2.5 eV lower than BCB. The CB states consist of 4p of Y mixed with 5d of Ce, even for the wavefunctions (WFS) of Ed under BCB there are still 24% of Y-4p and 9% of F-2p as components. Furthermore, transition state (TS) calculation was performed in this work to obtain the 4f→5d transition energies Efd, to improve the calculation of Ref.[6] in which a small CeF8 cluster embedded in an array of point charge was used and the results of ground-state calculation were roughly used to compare directly with the observed 4f→5d transition energies. The ionic radius of Ce3+ is larger than that of Y3+, for modeling approximately the lattice relaxation, we simply let the eight fluorine ions of the nearest-neighbor and next-nearest-neighbor move out radially and simultaneously. As results, the CeY4Li8F24 cluster with 4.56% outward relaxation of the eight fluorines has the lowest total energy and gave satisfactory 4f→5d energies Efd, but the calculated ground-state Ed is 0.68 eV higher than BCB. For another cluster with 7.36% outward relaxation the Ed is 0.43 eV lower than BCB, which makes the observation of fine structure (including zero-phonon line) of the lowest 5d band understandable easier, but the splits between the transition energies Efd were not as good as the former. Therefore, we consider the relaxation is somehow around 4.56%～7.36% outward, not as large as 10%.
Uba, S.; Bonda, A.; Uba, L.; Bekenov, L. V.; Antonov, V. N.; Ernst, A.
2016-08-01
In this joint experimental and ab initio study, we focused on the influence of the chemical composition and martensite phase transition on the electronic, magnetic, optical, and magneto-optical properties of the ferromagnetic shape-memory Ni-Mn-Ga alloys. The polar magneto-optical Kerr effect (MOKE) spectra for the polycrystalline sample of the Ni-Mn-Ga alloy of Ni60Mn13Ga27 composition were measured by means of the polarization modulation method over the photon energy range 0.8 ≤h ν ≤5.8 eV in magnetic field up to 1.5 T. The optical properties (refractive index n and extinction coefficient k ) were measured directly by spectroscopic ellipsometry using the rotating analyzer method. To complement experiments, extensive first-principles calculations were made with two different first-principles approaches combining the advantages of a multiple scattering Green function method and a spin-polarized fully relativistic linear-muffin-tin-orbital method. The electronic, magnetic, and MO properties of Ni-Mn-Ga Heusler alloys were investigated for the cubic austenitic and modulated 7M-like incommensurate martensitic phases in the stoichiometric and off-stoichiometric compositions. The optical and MOKE properties of Ni-Mn-Ga systems are very sensitive to the deviation from the stoichiometry. It was shown that the ab initio calculations reproduce well experimental spectra and allow us to explain the microscopic origin of the Ni2MnGa optical and magneto-optical response in terms of interband transitions. The band-by-band decomposition of the Ni2MnGa MOKE spectra is presented and the interband transitions responsible for the prominent structures in the spectra are identified.
Yang, Jian; Huang, Jihua; Fan, Dongyu; Chen, Shuhai; Zhao, Xingke
2016-05-01
First-principle calculations have been performed to investigate the structural, mechanical, thermo-physical and electronic properties of η‧-(CuNi)6Sn5 intermetallic compounds. The results indicated that, the doped Ni atom can not only enhance the stability of the η‧-Cu6Sn5, but also improve the mechanical and thermo-physical properties, which are more dependent on the Ni atom doping number than the doping position. In all the η‧-(CuNi)6Sn5, Cu3Ni3Sn5 (Cu1+Cu3 site) shows the best stability, the most excellent deformation resistance and the highest hardness. The Cu6Sn5, Cu3Ni3Sn5, Cu4Ni2Sn5, Cu1Ni5Sn5 and Ni6Sn5 are ductile while the Cu5Ni1Sn5 and Cu4Ni2Sn5 are brittle. The anisotropies of η‧-(CuNi)6Sn5 are all mainly due to the uneven distribution of Young's modulus at (001) planes, moreover, the anisotropy of Cu1Ni5Sn5 (Cu1+Cu2+Cu4 site) is the strongest while that of Ni6Sn5 is the weakest. The calculated Debye temperature and heat capacity showed that Cu4Ni2Sn5 (Cu2 site) possesses the best thermal conductivity (ΘD = 356.9 K) and Cu2Ni4Sn5 (Cu1+Cu2 site) possesses the largest heat capacity. From the electronic property analysis results, the Ni s and Ni p states can replace the Cu s and Cu p states to hybridize with Sn s states at -7.98 eV. Moreover, with the increasing number of the doped Ni atom, the hybridization between Cu d states at different positions is receded, while that between Ni d states is enhanced gradually.
Program Calculates Power Demands Of Electronic Designs
Cox, Brian
1995-01-01
CURRENT computer program calculates power requirements of electronic designs. For given design, CURRENT reads in applicable parts-list file and file containing current required for each part. Program also calculates power required for circuit at supply potentials of 5.5, 5.0, and 4.5 volts. Written by use of AWK utility for Sun4-series computers running SunOS 4.x and IBM PC-series and compatible computers running MS-DOS. Sun version of program (NPO-19590). PC version of program (NPO-19111).
Giffin, Nick A; Hendsbee, Arthur D; Roemmele, Tracey L; Lumsden, Michael D; Pye, Cory C; Masuda, Jason D
2012-11-01
A new, easily synthesized diphosphine based on a heterocyclic 1,3,2-diazaphospholidine framework has been prepared. Due to the large, sterically encumbering Dipp groups (Dipp = 2,6-diisopropylphenyl) on the heterocyclic ring, the diphosphine undergoes homolytic cleavage of the P-P bond in solution to form two phosphinyl radicals. The diphosphine has been reacted with O(2), S(8), Se, Te, and P(4), giving products that involve insertion of elements between the P-P bond to yield the related phosphinic acid anhydride, sulfide/disulfide, selenide, telluride, and a butterfly-type perphospha-bicyclobutadiene structure with a trans,trans-geometry. All molecules have been characterized by multinuclear NMR spectroscopy, elemental analysis, and single-crystal X-ray crystallography. Variable-temperature EPR spectroscopy was utilized to study the nature of the phosphinyl radical in solution. Electronic structure calculations were performed on a number of systems from the parent diphosphine [H(2)P](2) to amino-substituted [(H(2)N)(2)P](2) and cyclic amino-substituted [(H(2)C)(2)(NH)(2)P](2); then, bulky substituents (Ph or Dipp) were attached to the cyclic amino systems. Calculations on the isolated diphosphine at the B3LYP/6-31+G* level show that the homolytic cleavage of the P-P bond to form two phosphinyl radicals is favored over the diphosphine by ~11 kJ/mol. Furthermore, there is a significant amount of relaxation energy stored in the ligands (52.3 kJ/mol), providing a major driving force behind the homolytic cleavage of the central P-P bond.
Electron mobility calculation for graphene on substrates
Energy Technology Data Exchange (ETDEWEB)
Hirai, Hideki; Ogawa, Matsuto [Department of Electrical and Electronic Engineering, Graduate School of Engineering, Kobe University, 1-1, Rokko-dai, Nada-ku, Kobe 657-8501 (Japan); Tsuchiya, Hideaki, E-mail: tsuchiya@eedept.kobe-u.ac.jp [Department of Electrical and Electronic Engineering, Graduate School of Engineering, Kobe University, 1-1, Rokko-dai, Nada-ku, Kobe 657-8501 (Japan); Japan Science and Technology Agency, CREST, Chiyoda, Tokyo 102-0075 (Japan); Kamakura, Yoshinari; Mori, Nobuya [Japan Science and Technology Agency, CREST, Chiyoda, Tokyo 102-0075 (Japan); Division of Electrical, Electronic and Information Engineering, Graduate School of Engineering, Osaka University, Suita, Osaka 565-0871 (Japan)
2014-08-28
By a semiclassical Monte Carlo method, the electron mobility in graphene is calculated for three different substrates: SiO{sub 2}, HfO{sub 2}, and hexagonal boron nitride (h-BN). The calculations account for polar and non-polar surface optical phonon (OP) scatterings induced by the substrates and charged impurity (CI) scattering, in addition to intrinsic phonon scattering in pristine graphene. It is found that HfO{sub 2} is unsuitable as a substrate, because the surface OP scattering of the substrate significantly degrades the electron mobility. The mobility on the SiO{sub 2} and h-BN substrates decreases due to CI scattering. However, the mobility on the h-BN substrate exhibits a high electron mobility of 170 000 cm{sup 2}/(V·s) for electron densities less than 10{sup 12 }cm{sup −2}. Therefore, h-BN should be an appealing substrate for graphene devices, as confirmed experimentally.
Energy Technology Data Exchange (ETDEWEB)
Li, Jia; Zhang, Shengli [Division of Molecule and Materials Simulation, State Key Laboratory of Organic-Inorganic Composites, Beijing University of Chemical Technology, Beijing 100029 (China); Huang, Shiping, E-mail: huangsp@mail.buct.edu.cn [Division of Molecule and Materials Simulation, State Key Laboratory of Organic-Inorganic Composites, Beijing University of Chemical Technology, Beijing 100029 (China); Wang, Peng; Tian, Huiping [Research Institute of Petroleum Processing, SINOPEC , Beijing 100083 (China)
2013-02-15
R{sub 3}ZnH{sub 5} (R=K, Rb, Cs) series have been investigated with respect to the crystal structure, electronic and thermodynamic properties using first-principle methods based on density functional theory with generalized gradient approximation. The optimized structures and atomic coordinates are in good agreement with the experimental data. The strong covalent interactions are obtained between Zn and H atoms in the 18-electron [ZnH{sub 4}]{sup 2-} complex, while an ionic interaction is found between [ZnH{sub 4}]{sup 2-} and R atom. The formation enthalpies show that the formations of R{sub 3}ZnH{sub 5} hydrides are all exothermic at 298 K. The vibration free energies of R{sub 3}ZnH{sub 5} show that the thermodynamic stabilities of R{sub 3}ZnH{sub 5} hydrides decrease with the increasing diameter of R atom. Two possible decomposition reactions of R{sub 3}ZnH{sub 5} series have been suggested in our work. One (reaction one) is that R{sub 3}ZnH{sub 5} hydrides decomposes to elements directly, and the other (reaction two) is that R{sub 3}ZnH{sub 5} hydrides decomposes to RH hydride. The results show that the first decomposition reaction is more favorable one. The spontaneous decomposition reaction of K{sub 3}ZnH{sub 5} hydrides occur upon 465 K via reaction one, and 564 K via reaction two, respectively. - Graphical abstract: Total charge density of K{sub 3}ZnH{sub 5}. Highlights: Black-Right-Pointing-Pointer Electronic and thermodynamic properties of R{sub 3}ZnH{sub 5} (R=K, Rb, Cs) were calculated. Black-Right-Pointing-Pointer The formations of R{sub 3}ZnH{sub 5} hydrides are all exothermic at 298 K. Black-Right-Pointing-Pointer The thermodynamic stabilities decrease with the increasing diameter of R atom. Black-Right-Pointing-Pointer Two possible decomposition pathways of R{sub 3}ZnH{sub 5} were investigated.
Institute of Scientific and Technical Information of China (English)
Sheng Chun-Qi; Wang Peng; Shen Ying; Li Yan-Jun; Zhang Wen-Hua; Xu Fa-Qiang; Zhu Jun-Fa; Li Hong-Nian; Lai Guo-Qiao
2012-01-01
We have studied the electronic structure of [6,6]-phenyl-C61-butyric-acid-methyl-ester (PCBM) using synchrotron radiation photoelectron spectroscopy (PES) measurements and first-principles calculations.The PES spectrum of the entire occupied valence band is reported,which exhibits abundant spectral features from the Fermi level to ～ 24 eV binding energy. All the spectral features are broadened as compared with the cases of C60. The reasons for the broadening are analysed by comparing the experimental data with the calculated energy levels and density of states.Special attention is paid to the analysis of the C60 highest occupied molecular orbital (HOMO)-1 derived states,which can play a crucial role in the bonding at the interfaces of PCBM/polymer blenders or PCBM/electrodes.Besides the well-known energy level splitting of the C60 backbone caused by the lowered symmetry,C 2p states from the side chain mix or hybridize with the molecular orbitals of parent C60.The contribution of the O 2p states can substantially modify the PES spectrum.
Demkov, Alexander A.; Navrotsky, Alexandra
2001-03-01
The International Technology Roadmap for Semiconductors (ITRS) predicts that the strategy of scaling complementary metal-oxide-semiconductor (CMOS) devices will come to an abrupt end around the year 2012. The main reason for this will be the unacceptably high leakage current through the silicon dioxide gate with a thickness below 20 ÅFinding a gate insulator alternative to SiO2 has proven to be far from trivial. Hafnium and zirconium dioxides and silicates have been recently considered as gate dielectrics with intermediate dielectric constants. Hafnia and ziconia are important ceramic materials as well, and their phase relations are rather well studied. There is also interest in hafnia as a constituent of ceramic waste forms for plutonium, based on its refractory nature and high neutron absorption cross section. We use a combination of the ab-initio calculations and calorimetry to investigate thermodynamic and electronic properties of hafnia and zirconia. We describe the cubic to tetragonal phase transition in the fluorite structure by computing the total energy surface for zone-edge distortions correct to fourth order in the soft-mode displacement with the strain coupling renormalization included. We compare the two materials using some simple chemical concepts.
A corrector for spacecraft calculated electron moments
Directory of Open Access Journals (Sweden)
J. Geach
2005-03-01
Full Text Available We present the application of a numerical method to correct electron moments calculated on-board spacecraft from the effects of potential broadening and energy range truncation. Assuming a shape for the natural distribution of the ambient plasma and employing the scalar approximation, the on-board moments can be represented as non-linear integral functions of the underlying distribution. We have implemented an algorithm which inverts this system successfully over a wide range of parameters for an assumed underlying drifting Maxwellian distribution. The outputs of the solver are the corrected electron plasma temperature T_{e}, density N_{e} and velocity vector V_{e}. We also make an estimation of the temperature anisotropy A of the distribution. We present corrected moment data from Cluster's PEACE experiment for a range of plasma environments and make comparisons with electron and ion data from other Cluster instruments, as well as the equivalent ground-based calculations using full 3-D distribution PEACE telemetry.
Azadegan, B.
2013-03-01
The presented Mathematica code is an efficient tool for simulation of planar channeling radiation spectra of relativistic electrons channeled along major crystallographic planes of a diamond-structure single crystal. The program is based on the quantum theory of channeling radiation which has been successfully applied to study planar channeling at electron energies between 10 and 100 MeV. Continuum potentials for different planes of diamond, silicon and germanium single crystals are calculated using the Doyle-Turner approximation to the atomic scattering factor and taking thermal vibrations of the crystal atoms into account. Numerical methods are applied to solve the one-dimensional Schrödinger equation. The code is designed to calculate the electron wave functions, transverse electron states in the planar continuum potential, transition energies, line widths of channeling radiation and depth dependencies of the population of quantum states. Finally the spectral distribution of spontaneously emitted channeling radiation is obtained. The simulation of radiation spectra considerably facilitates the interpretation of experimental data. Catalog identifier: AEOH_v1_0 Program summary URL:http://cpc.cs.qub.ac.uk/summaries/AEOH_v1_0.html Program obtainable from: CPC Program Library, Queen's University, Belfast, N. Ireland Licensing provisions: Standard CPC licence, http://cpc.cs.qub.ac.uk/licence/licence.html No. of lines in distributed program, including test data, etc.: 446 No. of bytes in distributed program, including test data, etc.: 209805 Distribution format: tar.gz Programming language: Mathematica. Computer: Platforms on which Mathematica is available. Operating system: Operating systems on which Mathematica is available. RAM: 1 MB Classification: 7.10. Nature of problem: Planar channeling radiation is emitted by relativistic charged particles during traversing a single crystal in direction parallel to a crystallographic plane. Channeling is modeled as the motion
Epifanovsky, Evgeny; Wormit, Michael; Kuś, Tomasz; Landau, Arie; Zuev, Dmitry; Khistyaev, Kirill; Manohar, Prashant; Kaliman, Ilya; Dreuw, Andreas; Krylov, Anna I
2013-10-05
This article presents an open-source object-oriented C++ library of classes and routines to perform tensor algebra.The primary purpose of the library is to enable post-Hartree–Fock electronic structure methods; however, the code is general enough to be applicable in other areas of physical and computational sciences. The library supports tensors of arbitrary order (dimensionality), size, and symmetry. Implemented data structures and algorithms operate on large tensors by splitting them into smaller blocks, storing them both in core memory and in files on disk, and applying divide-and-conquer-type parallel algorithms to perform tensor algebra. The library offers a set of general tensor symmetry algorithms and a full implementation of tensor symmetries typically found in electronic structure theory: permutational, spin, and molecular point group symmetry. The Q-Chem electronic structure software uses this library to drive coupled-cluster, equation-of-motion, and algebraic-diagrammatic construction methods.
First Principles Calculations of Electronic Excitations in 2D Materials
DEFF Research Database (Denmark)
Rasmussen, Filip Anselm
-thin electronics and high efficiency solar cells. Contrary to many other nano-materials, methods for large scale fabrication and patterning have already been demonstrated and the first real technological applications have already be showcased. Still the technology is very young and the number of well-studied 2D...... materials are few. However as the list of 2D materials is growing it is necessary to investigate their fundamental structural, electronic and optical properties. These are determined by the atomic and electronic structure of the materials that can quite accurately predicted by computational quantum...... as if it is being screened by the electrons in the material. This method has been very successful for calculating quasiparticle energies of bulk materials but results have been more varying for 2D materials. The reason is that the 2D confined electrons are less able to screen the added charge and some...
The calculation of vibrational intensities in forbidden electronic transitions.
Johnson, Philip M; Xu, Haifeng; Sears, Trevor J
2006-10-28
A method is described for the use of electronic structure and Franck-Condon factor programs in the calculation of the vibrational intensities in forbidden electronic transitions. Using the B 2B2-X 2B1 electronic transition of benzonitrile cation as a test case, transition moments were calculated using the symmetry adapted cluster/configuration interaction method at various points along the normal mode displacements of the molecule, from which transition moment derivatives were obtained. The transition moments were found to vary almost linearly with respect to the normal mode displacements. Using these, along with Franck-Condon factors, an expansion of the transition moment with respect to the normal coordinates provides a measure of vibrational intensities, including the effects of geometry change and Duschinsky rotation [Acta Physicochim. URSS 7, 551 (1937)]. Second order terms in the moment expansion are calculated, and it is determined that they must be included if the intensity of combination bands is to be properly obtained.
Calculation of fractional electron capture probabilities
Schoenfeld, E
1998-01-01
A 'Table of Radionuclides' is being prepared which will supersede the 'Table de Radionucleides' formerly issued by the LMRI/LPRI (France). In this effort it is desirable to have a uniform basis for calculating theoretical values of fractional electron capture probabilities. A table has been compiled which allows one to calculate conveniently and quickly the fractional probabilities P sub K , P sub L , P sub M , P sub N and P sub O , their ratios and the assigned uncertainties for allowed and non-unique first forbidden electron capture transitions of known transition energy for radionuclides with atomic numbers from Z=3 to 102. These results have been applied to a total of 28 transitions of 14 radionuclides ( sup 7 Be, sup 2 sup 2 Na, sup 5 sup 1 Cr, sup 5 sup 4 Mn, sup 5 sup 5 Fe, sup 6 sup 8 Ge , sup 6 sup 8 Ga, sup 7 sup 5 Se, sup 1 sup 0 sup 9 Cd, sup 1 sup 2 sup 5 I, sup 1 sup 3 sup 9 Ce, sup 1 sup 6 sup 9 Yb, sup 1 sup 9 sup 7 Hg, sup 2 sup 0 sup 2 Tl). The values are in reasonable agreement with measure...
Using electron microscopy to calculate optical properties of biological samples
Wu, Wenli; Radosevich, Andrew J.; Eshein, Adam; Nguyen, The-Quyen; Yi, Ji; Cherkezyan, Lusik; Roy, Hemant K.; Szleifer, Igal; Backman, Vadim
2016-01-01
The microscopic structural origins of optical properties in biological media are still not fully understood. Better understanding these origins can serve to improve the utility of existing techniques and facilitate the discovery of other novel techniques. We propose a novel analysis technique using electron microscopy (EM) to calculate optical properties of specific biological structures. This method is demonstrated with images of human epithelial colon cell nuclei. The spectrum of anisotropy...
Yu, Jen-Shiang K; Hwang, Jenn-Kang; Tang, Chuan Yi; Yu, Chin-Hui
2004-01-01
A number of recently released numerical libraries including Automatically Tuned Linear Algebra Subroutines (ATLAS) library, Intel Math Kernel Library (MKL), GOTO numerical library, and AMD Core Math Library (ACML) for AMD Opteron processors, are linked against the executables of the Gaussian 98 electronic structure calculation package, which is compiled by updated versions of Fortran compilers such as Intel Fortran compiler (ifc/efc) 7.1 and PGI Fortran compiler (pgf77/pgf90) 5.0. The ifc 7.1 delivers about 3% of improvement on 32-bit machines compared to the former version 6.0. Performance improved from pgf77 3.3 to 5.0 is also around 3% when utilizing the original unmodified optimization options of the compiler enclosed in the software. Nevertheless, if extensive compiler tuning options are used, the speed can be further accelerated to about 25%. The performances of these fully optimized numerical libraries are similar. The double-precision floating-point (FP) instruction sets (SSE2) are also functional on AMD Opteron processors operated in 32-bit compilation, and Intel Fortran compiler has performed better optimization. Hardware-level tuning is able to improve memory bandwidth by adjusting the DRAM timing, and the efficiency in the CL2 mode is further accelerated by 2.6% compared to that of the CL2.5 mode. The FP throughput is measured by simultaneous execution of two identical copies of each of the test jobs. Resultant performance impact suggests that IA64 and AMD64 architectures are able to fulfill significantly higher throughput than the IA32, which is consistent with the SpecFPrate2000 benchmarks.
Guo, San-Dong
2016-05-01
To identify thermoelectric materials containing abundant, low-cost and non-toxic elements, we have studied the electronic structures and thermoelectric properties of (Mg2X)2/ (Mg2Y)2 (X, Y = Si, Ge, Sn) superlattices with state-of-the-art first-principles calculations using a modified Becke and Johnson (mBJ) exchange potential. Our results show that (Mg2Ge)2/ (Mg2Sn)2 and (Mg2Si)2/ (Mg2Sn)2 are semi-metals using mBJ plus spin-orbit coupling (mBJ + SOC), while (Mg2Si)2/ (Mg2Ge)2 is predicted to be a direct-gap semiconductor with a mBJ gap value of 0.46 eV and mBJ + SOC gap value of 0.44 eV. Thermoelectric properties are predicted by through solving the Boltzmann transport equations within the constant scattering time approximation. It is found that (Mg2Si)2/ (Mg2Ge)2 has a larger Seebeck coefficient and power factor than (Mg2Ge)2/ (Mg2Sn)2 and (Mg2Si)2/ (Mg2Sn)2 for both p-type and n-type doping. The detrimental influence of SOC on the power factor of p-type (Mg2X)2/ (Mg2Y)2 (X, Y = Si, Ge, Sn) is analyzed as a function of the carrier concentration, but there is a negligible SOC effect for n-type. These results can be explained by the influence of SOC on their valence and conduction bands near the Fermi level.
Energy Technology Data Exchange (ETDEWEB)
Evarestov, R A; Panin, A I; Bandura, A V; Losev, M V [Department of Quantum Chemistry, St. Petersburg State University, University Prospect 26, Stary Peterghof, St. Petersburg, 198504 (Russian Federation)], E-mail: re1973@re1973.spb.edu
2008-06-01
The results of LCAO DFT calculations of lattice parameters, cohesive energy and bulk modulus of the crystalline uranium nitrides UN, U{sub 2}N{sub 3} and UN{sub 2} are presented and discussed. The LCAO computer codes Gaussian03 and Crystal06 are applied. The calculations are made with the uranium atom relativistic effective small core potential by Stuttgart-Cologne group (60 electrons in the core). The calculations include the U atom basis set optimization. Powell, Hooke-Jeeves, conjugated gradient and Box methods are implemented in the author's optimization package, being external to the codes for molecular and periodic calculations. The basis set optimization in LCAO calculations improves the agreement of the lattice parameter and bulk modulus of UN crystal with the experimental data, the change of the cohesive energy due to the optimization is small. The mixed metallic-covalent chemical bonding is found both in LCAO calculations of UN and U{sub 2}N{sub 3} crystals; UN{sub 2} crystal has the semiconducting nature.
Masrour, R.; Hlil, E. K.
2016-08-01
Self-consistent ab initio calculations based on density-functional theory and using both full potential linearized augmented plane wave and Korring-Kohn-Rostoker-coherent potential approximation methods, are performed to investigate both electronic and magnetic properties of the Ga1-xMnxN system. Magnetic moments considered to lie along (001) axes are computed. Obtained data from ab initio calculations are used as input for the high temperature series expansions (HTSEs) calculations to compute other magnetic parameters such as the magnetic phase diagram and the critical exponent. The increasing of the dilution x in this system has allowed to verify a series of HTSEs predictions on the possibility of ferromagnetism in dilute magnetic insulators and to demonstrate that the interaction changes from antiferromagnetic to ferromagnetic passing through the spins glace phase.
Energy Technology Data Exchange (ETDEWEB)
Masrour, R., E-mail: rachidmasrour@hotmail.com [Laboratory of Materials, Processes, Environment and Quality, Cady Ayyed University, National School of Applied Sciences, 63 46000, Safi (Morocco); LMPHE (URAC 12), Faculty of Science, Mohammed V-Agdal University, Rabat (Morocco); Hlil, E.K. [Institut Néel, CNRS et Université Joseph Fourier, BP 166, F-38042 Grenoble cedex 9 (France); Hamedoun, M. [Institute of Nanomaterials and Nanotechnologies, MAScIR, Rabat (Morocco); Benyoussef, A. [LMPHE (URAC 12), Faculty of Science, Mohammed V-Agdal University, Rabat (Morocco); Institute of Nanomaterials and Nanotechnologies, MAScIR, Rabat (Morocco); Hassan II Academy of Science and Technology, Rabat (Morocco); Mounkachi, O.; El Moussaoui, H. [Institute of Nanomaterials and Nanotechnologies, MAScIR, Rabat (Morocco)
2015-03-15
Self-consistent ab initio calculations, based on density functional theory (DFT) approach and using a full potential linear augmented plane wave (FLAPW) method, are performed to investigate both electronic and magnetic properties of the Fe{sub 3}O{sub 4}. Polarized spin and spin–orbit coupling are included in calculations within the framework of the antiferromagnetic state between two adjacent Fe plans. Magnetic moment considered to lie along (010) axes are computed. Obtained data from ab initio calculations are used as input for the high temperature series expansions (HTSEs) calculations to compute other magnetic parameters. The exchange interactions between the magnetic atoms Fe–Fe in Fe{sub 3}O{sub 4} are given using the mean field theory. The high temperature series expansions (HTSEs) of the magnetic susceptibility of with the magnetic moments, m{sub Fe} in Fe{sub 3}O{sub 4} is given up to seventh order series in (1/k{sub B}T). The Néel temperature T{sub N} is obtained by HTSEs of the magnetic susceptibility series combined with the Padé approximant method. The critical exponent γ associated with the magnetic susceptibility is deduced as well. - Highlights: • Ab initio calculations, based on DFT approach and FLAPW are used to study the electronic properties of Fe{sub 3}O{sub 4}. • Magnetic moments of Fe{sub 1} and Fe{sub 2} are estimated to −/+3.44 µ{sub B}. • HTSE method is used to calculate the Néel temperature of Fe{sub 3}O{sub 4}.
Electronic structure of tin monosulfide
Bletskan, D. I.; Bletskan, M. M.; Glukhov, K. E.
2017-01-01
The band structure of three-dimensional and two-dimensional tin monosulfide was calculated by the density functional method in LDA and LDA+U approximations. Group-theoretical analysis of the electronic band structure of SnS crystallized in the orthorhombic structure with space group D2h16- Pcmn is carried out, the symmetry of wave functions of the valence band and the bottom of the conduction band is found. The selection rules for direct and indirect optical transitions at different incident light polarization are determined. The group-theoretical analysis of energy states of the three-dimensional and two-dimensional SnS structures explains the formation of the band structure including the Davydov splitting. The calculated total density of states is compared with the known experimental XPS and UPS spectra, providing the assignment of their main features.
Fast Electron Beam Simulation and Dose Calculation
Trindade, A; Peralta, L; Lopes, M C; Alves, C; Chaves, A
2003-01-01
A flexible multiple source model capable of fast reconstruction of clinical electron beams is presented in this paper. A source model considers multiple virtual sources emulating the effect of accelerator head components. A reference configuration (10 MeV and 10x10 cm2 field size) for a Siemens KD2 linear accelerator was simulated in full detail using GEANT3 Monte Carlo code. Our model allows the reconstruction of other beam energies and field sizes as well as other beam configurations for similar accelerators using only the reference beam data. Electron dose calculations were performed with the reconstructed beams in a water phantom and compared with experimental data. An agreement of 1-2% / 1-2 mm was obtained, equivalent to the accuracy of full Monte Carlo accelerator simulation. The source model reduces accelerator simulation CPU time by a factor of 7500 relative to full Monte Carlo approaches. The developed model was then interfaced with DPM, a fast radiation transport Monte Carlo code for dose calculati...
Muthu, S; Elamuruguporchelvi, E; Varghese, Anitha
2015-03-05
The solid phase FTIR and FT-Raman spectra of 2-[(5-nitro-1,3-thiazol-2-yl)carbamoyl]phenyl acetate (25N2LCPA) have been recorded 450-4000cm(-1) and 100-4000cm(-1) respectively. The normal coordinate analysis was carried out to confirm the precision of the assignments. DFT calculations have been performed giving energies, optimized structures, harmonic vibrational frequencies and IR intensities. The structure of the molecule was optimized and the structural characteristics were determined by density functional theory (DFT) using B3LYP method with 6-31+G(d,p) basis set. The detailed interpretation of the vibrational spectra has been carried out with aid of normal coordinate analysis (NCA) following the scaled quantum mechanical force field methodology. The Vibrational frequencies are calculated in the above method and are compared with experimental frequencies which yield good agreement between observed and calculated frequencies. Stability of the molecule arising from hyper conjugative interactions, charge delocalization has been analyzed using natural bond orbital (NBO) analysis. In addition, Frontiers molecular orbital and molecular electrostatic potential were computed by using Density Functional Theory (DFT) B3LYP/6-31+G(d,p) basis set. The calculated HOMO and LUMO energies show that charge transfer occurs in the molecule.
First-Principles Calculations of Electron Transfer in Organic Molecules
Pati, Ranjit; Karna, Shashi P.
2000-03-01
Suitably tailored organic structures are considered potential candidates as components in molecular electronic devices. A common molecular architecture for electronics consists of an electron donor (D) and an electron acceptor (A) moiety bonded together by a chemically inert bridging moiety, called spacer (S). The D-S-A combination constitutes the basic component equivalent of a solid state capacitor. A useful physical property that determines the applicability of molecular structures in moletronics is the electron transfer (ET) rate, which is related, in a two-state approximation, to the coupling matrix between the two electronic states representing the localization of electrons. In an effort to model potential organic structures, we have calculated the ET coupling matrix elements in a number of D-, S-, and A-type organic molecules with the use of ab initio Hartree-Fock method and two different basis sets, namely an STO-3G and a double zeta plus polarization (DZP). A number of important findings have emerged from this study: (i) The ET coupling matrix strongly depends upon the geometrical arrangement of the molecular fragment(s) in the architecture. (ii) In an oligomeric chain, the ET matrix decreases exponentially with molecular length (number of monomer units). (iii) In cyclic alkanes, the magnitude of the ET coupling matrix decreases with increasing size of fused rings.
Electronic structure of BaFe{sub 2}As{sub 2} as obtained from DFT/ASW first-principles calculations
Energy Technology Data Exchange (ETDEWEB)
Schwingenschloegl, U.; Di Paola, C. [KAUST, PSE Division, Thuwal (Saudi Arabia)
2010-08-15
We use ab-initio calculations based on the augmented spherical wave method within density functional theory to study the magnetic ordering and Fermi surface of BaFe{sub 2}As{sub 2}, the parent compound of the hole-doped iron pnictide superconductors (K,Ba)Fe{sub 2}As{sub 2}, for the tetragonal I4/mmm as well as the orthorhombic Fmmm structure. In comparison to full potential linear augmented plane wave calculations, we obtain significantly smaller magnetic energies. This finding is remarkable, since the augmented spherical wave method, in general, is known for a most reliable description of magnetism. (Abstract Copyright [2010], Wiley Periodicals, Inc.)
Global nuclear-structure calculations
Energy Technology Data Exchange (ETDEWEB)
Moeller, P.; Nix, J.R.
1990-04-20
The revival of interest in nuclear ground-state octupole deformations that occurred in the 1980's was stimulated by observations in 1980 of particularly large deviations between calculated and experimental masses in the Ra region, in a global calculation of nuclear ground-state masses. By minimizing the total potential energy with respect to octupole shape degrees of freedom in addition to {epsilon}{sub 2} and {epsilon}{sub 4} used originally, a vastly improved agreement between calculated and experimental masses was obtained. To study the global behavior and interrelationships between other nuclear properties, we calculate nuclear ground-state masses, spins, pairing gaps and {Beta}-decay and half-lives and compare the results to experimental qualities. The calculations are based on the macroscopic-microscopic approach, with the microscopic contributions calculated in a folded-Yukawa single-particle potential.
Electronic structure of herbicides: Atrazine and bromoxynil
Novak, Igor; Kovač, Branka
2011-06-01
The electronic structures of herbicides atrazine and bromoxynil have been investigated by UV photoelectron spectroscopy (UPS), quantum chemical calculations and comparison with X-ray diffraction, molecular docking and molecular dynamics studies. Their electronic and molecular structures are discussed in the context of their biological activity. This is the first report which correlates the molecular mechanism of biological activity of these herbicides with their experimentally determined electronic and molecular structures.
Directory of Open Access Journals (Sweden)
Moulay N.
2015-06-01
Full Text Available The full potential linear-muffin-tin-orbital method within the spin local density approximation has been used to study the structural, electronic, magnetic and thermodynamic properties of three multiferroic compounds of XFeO3 type. Large values of bulk modulus for these compounds have been obtained, which demonstrates their hardness. The calculated total and partial density of states of these compounds shows a complex of strong hybridized 3d and 4d states at Fermi level. The two degenerate levels eg and t2g clearly demonstrate the origin of this complex. We have also investigated the effect of pressure, from 0 GPa to 55 GPa, on the magnetic moment per atom and the exchange of magnetic energy between the ferromagnetic and antiferromagnetic states. For more detailed knowledge, we have calculated the thermodynamic properties, and determined heat capacity, Debye temperature, bulk modulus and enthropy at different temperatures and pressures for the three multiferroic compounds. This is the first predictive calculation of all these properties.
Indian Academy of Sciences (India)
Feng Wen-Lin; Zheng Wen-Chen
2008-09-01
By calculating the optical spectrum band positions and EPR parameters ( factors, ∥, ⊥ and zero-field splitting ) by diagonalizing the complete energy matrix of 3d8 ions in trigonal symmetry, the defect structure of Ni2+ centre in -LiIO3 crystal is studied. It is found that to reach the good fits of optical and EPR data between calculation and experiment, the Ni2+ ion should shift by ≈ 0.298 Å along C3 -axis and the O2− ions between the Ni2+ ion and Li+ vacancy (Li) should be displaced away from the Li by ≈ 0.097 Å because of the electrostatic interaction. The results are discussed.
Mátyus, Edit; Reiher, Markus
2012-07-14
We elaborate on the theory for the variational solution of the Schrödinger equation of small atomic and molecular systems without relying on the Born-Oppenheimer paradigm. The all-particle Schrödinger equation is solved in a numerical procedure using the variational principle, Cartesian coordinates, parameterized explicitly correlated Gaussian functions with polynomial prefactors, and the global vector representation. As a result, non-relativistic energy levels and wave functions of few-particle systems can be obtained for various angular momentum, parity, and spin quantum numbers. A stochastic variational optimization of the basis function parameters facilitates the calculation of accurate energies and wave functions for the ground and some excited rotational-(vibrational-)electronic states of H(2) (+) and H(2), three bound states of the positronium molecule, Ps(2), and the ground and two excited states of the (7)Li atom.
Electronic structure and polarizability of metallic nanoshells
Prodan, E.; Nordlander, P.
2002-01-01
An efficient method for the calculation of the electronic structure of metallic nanoshells is developed. The method is applied to a large nanoshell (of 10 nm in diameter) containing more than 2.5×10 4 conduction electrons. The calculations show that the density of states of the nanoshell is relatively bulk-like. The frequency dependent polarizability is calculated and shown to display strong confinement effects and features similar to what is predicted by semi-classical electrodynamic theory.
Computational Chemistry Using Modern Electronic Structure Methods
Bell, Stephen; Dines, Trevor J.; Chowdhry, Babur Z.; Withnall, Robert
2007-01-01
Various modern electronic structure methods are now days used to teach computational chemistry to undergraduate students. Such quantum calculations can now be easily used even for large size molecules.
Dinca, Nicolae; Dragan, Simona; Dinca, Mihael; Sisu, Eugen; Covaci, Adrian
2014-05-20
Differential mass spectrometry correlated with quantum chemical calculations (QCC-ΔMS) has been shown to be an efficient tool for the chemical structure identification (CSI) of isomers with similar mass spectra. For this type of analysis, we report here a new strategy based on ordering (ORD), linear correlation (LCOR) algorithms, and their coupling, to filter the most probable structures corresponding to similar mass spectra belonging to a group with dozens of isomers (e.g., tetrachlorinated biphenyls, TeCBs). This strategy quantifies and compares the values of enthalpies of formation (Δ(f)H) obtained by QCC for some isobaric ions from the electron ionization (EI)-MS mass spectra, to the corresponding relative intensities. The result of CSI is provided in the form of lists of decreasing probabilities calculated for all the position-isomeric structures using the specialized software package CSI-Diff-MS Analysis 3.1.1. The simulation of CSI with ORD, LCOR, and their coupling of six TeCBs (IUPAC no. 44, 46, 52, 66, 74, and 77) has allowed us to find the best semiempirical molecular-orbital methods for several of their common isobaric fragments. The study of algorithms and strategy for the entire group of TeCBs (42 isomers) was made with one of the optimal variants for the computation of Δ(f)H using semiempirical molecular orbital methods of HyperChem: AM1 for M(+•) and [M - 4Cl](+•) ions and RM1 for [M - Cl](+) and [M - 2Cl](+•). The analytical performance of ORD, LCOR, and their coupling resulted from the CSI simulation of an analyte of known structure, using a decreasing number of isomeric standards, s = 5, 4, 3, and 2. Compared with the results obtained by a classical library search for TeCB isomers, the novel strategies of assigning structures of isomers with very similar mass spectra based on ORD, LCOR, and their coupling were much more efficient, because they provide the correct structure at the top of the probability list. Databases used in these CSI
Electronic Structure of Doped Trans-Polyacetylene
Institute of Scientific and Technical Information of China (English)
无
2002-01-01
The behavior of electronic structures of doped trans-polyacetylene is revealed by a simplemethod. (C24H26)+n is used to simulate p-type doped trans-polyacetylene at various doping concentrations.The electronic structure is calculated by CNDO/2 method. These calculations show that at low doping lev-el, the decrease of electronic energy compensates the increase of elastic energy, thus the bond alternationexists, and the charge carriers are solitons. When doping level is high, the increase of elastic energy islarger than the decrease of electronic energy, the bond alternation disappears, solitons no longer exist,and polyacetylene is in a metalic state.
Energy Technology Data Exchange (ETDEWEB)
Latosinska, J.N.; Kasprzak, J.; Mazurek, P.; Nogaj, B. [Inst. Fizyki, Univ. A. Mickiewicza, (Poland); Latosinska, M. [Politechnika Poznanska, Poznan (Poland)
1995-12-31
The {sup 35}Cl NQR as well as MNDO and INDO quantum chemistry calculation methods have been used for determination of electronic structure of selected benzo ditiazine derivatives. The most probable molecular conformation has been taken into account. Also molecular dynamics has been studied for hydro chloro thiazole. The resonant frequency temperature dependence has been measured in the range of 77 - 300 K. 7 refs, 6 figs, 3 tabs.
Energy Technology Data Exchange (ETDEWEB)
Wang, Xianlong, E-mail: WangXianlong@uestc.edu.cn, E-mail: pbeckman@brynmawr.edu [Key Laboratory for NeuroInformation of Ministry of Education, School of Life Science and Technology, University of Electronic Science and Technology of China, 4 North Jianshe Rd., 2nd Section, Chengdu 610054 (China); Mallory, Frank B. [Department of Chemistry, Bryn Mawr College, 101 North Merion Ave., Bryn Mawr, Pennsylvania 19010-2899 (United States); Mallory, Clelia W. [Department of Chemistry, Bryn Mawr College, 101 North Merion Ave., Bryn Mawr, Pennsylvania 19010-2899 (United States); Department of Chemistry, University of Pennsylvania, Philadelphia, Pennsylvania 19104-6323 (United States); Odhner, Hosanna R.; Beckmann, Peter A., E-mail: WangXianlong@uestc.edu.cn, E-mail: pbeckman@brynmawr.edu [Department of Physics, Bryn Mawr College, 101 North Merion Ave., Bryn Mawr, Pennsylvania 19010-2899 (United States)
2014-05-21
We report ab initio density functional theory electronic structure calculations of rotational barriers for t-butyl groups and their constituent methyl groups both in the isolated molecules and in central molecules in clusters built from the X-ray structure in four t-butyl aromatic compounds. The X-ray structures have been reported previously. We also report and interpret the temperature dependence of the solid state {sup 1}H nuclear magnetic resonance spin-lattice relaxation rate at 8.50, 22.5, and 53.0 MHz in one of the four compounds. Such experiments for the other three have been reported previously. We compare the computed barriers for methyl group and t-butyl group rotation in a central target molecule in the cluster with the activation energies determined from fitting the {sup 1}H NMR spin-lattice relaxation data. We formulate a dynamical model for the superposition of t-butyl group rotation and the rotation of the t-butyl group's constituent methyl groups. The four compounds are 2,7-di-t-butylpyrene, 1,4-di-t-butylbenzene, 2,6-di-t-butylnaphthalene, and 3-t-butylchrysene. We comment on the unusual ground state orientation of the t-butyl groups in the crystal of the pyrene and we comment on the unusually high rotational barrier of these t-butyl groups.
Energy Technology Data Exchange (ETDEWEB)
Wan, Chuan; Hu, Mary Y.; Jaegers, Nicholas R.; Shi, Dachuan; Wang, Huamin; Gao, Feng; Qin, Zhaohai; Wang, Yong; Hu, Jian Zhi
2016-10-13
The metal-support interaction in γ-Al2O3 supported WOX catalysts is investigated by a combination of high field quantitative single pulse (SP) 27Al MAS NMR spectroscopy, 2D MQMAS, 1H-27Al CP/MAS, and electronic structure calculations. NMR allows the observation of at least seven different Al sites, including a pentahedral Al site, three different tetrahedral Al sites, and three octahedral Al sites. It is found that the penta-coordinated Al (AlP) site density decreases monotonically with an increased WOX loading while the octahedral Al (AlO) site density increases concurrently. This suggests that the Alp sites are the preferred surface anchoring positions for the WOX species. Importantly, the AlP site isotropic chemical shift observed for the unsupported γ-Al2O3 at about 38 ppm migrates into the octahedral region with a new isotropic chemical shift value appearing near 7 ppm when the Alp site is anchored by WOX species. Density functional theory (DFT) computational modeling of the NMR parameters on proposed cluster models is carried out to accurately interpret the dramatic chemical shift changes from which the detailed anchoring mechanisms are obtained. It is found that tungsten dimers and monomers are the preferred supported surface species on γ-Al2O3, wherein one monomeric and several dimeric structures are identified as the most likely surface anchoring structures.
Using electron microscopy to calculate optical properties of biological samples.
Wu, Wenli; Radosevich, Andrew J; Eshein, Adam; Nguyen, The-Quyen; Yi, Ji; Cherkezyan, Lusik; Roy, Hemant K; Szleifer, Igal; Backman, Vadim
2016-11-01
The microscopic structural origins of optical properties in biological media are still not fully understood. Better understanding these origins can serve to improve the utility of existing techniques and facilitate the discovery of other novel techniques. We propose a novel analysis technique using electron microscopy (EM) to calculate optical properties of specific biological structures. This method is demonstrated with images of human epithelial colon cell nuclei. The spectrum of anisotropy factor g, the phase function and the shape factor D of the nuclei are calculated. The results show strong agreement with an independent study. This method provides a new way to extract the true phase function of biological samples and provides an independent validation for optical property measurement techniques.
Das, Debashish; Ganguly, Shreemoyee; Sanyal, Biplab; Ghosh, Subhradip
2016-10-01
CoCr2O4 has attracted significant attention recently due to several interesting properties such as magnetostriction, magnetoelectricity etc. More recent experiments on Fe substituted CoCr2O4 observed a variety of novel phenomena such as the magnetic compensation accompanied by the occurrence of exchange bias, which reverses its sign. Understanding of such phenomena may lead to control the properties of these material in an efficient way to enhance its potential for multifunctional applications. In this paper, we study the fundamental understanding of Fe doping in modifying the structural and magnetic properties of CoCr2O4 with varying composition and substitution of Fe at different sublattices by first-principles density functional calculations. We have analysed in detail the effect of Fe substitution on crystal field and exchange splittings, magnetic moments and interatomic exchange parameters. It is also observed that with increasing concentration of Fe impurity, the system has a tendency towards forming an ‘inverse spinel’ structure as observed in experiments. Such tendencies are crucial to understand this system as it would lead to modifications in the magnetic exchange interactions associated with sites with different symmetry finally affecting the magnetic structure and the multiferrocity in turn.
Electronic Structure of the Actinide Metals
DEFF Research Database (Denmark)
Johansson, B.; Skriver, Hans Lomholt
1982-01-01
Some recent experimental photoelectron spectroscopic results for the actinide metals are reviewed and compared with the theoretical picture of the basic electronic structure that has been developed for the actinides during the last decade. In particular the experimental data confirm the change from...... itinerant to localized 5f electron behaviour calculated to take place between plutonium and americium. From experimental data it is shown that the screening of deep core-holes is due to 5f electrons for the lighter actinide elements and 6d electrons for the heavier elements. A simplified model for the full...... LMTO electronic structure calculations is introduced. In this model the spd and 5f electronic contributions are treated as separable entities. It is shown that the model reproduces quite well the results from the full treatment. The equilibrium volume, cohesive energy and bulk modulus are calculated...
Waller, Sarah E; Mann, Jennifer E; Hossain, Ekram; Troyer, Mary; Jarrold, Caroline C
2012-07-14
Vibrationally-resolved photoelectron spectra of AlMoO(y)(-) (y = 1-4) are presented and analyzed in conjunction with density functional theory computational results. The structures determined for the AlMoO(y) anion and neutral clusters suggest ionic bonding between Al(+) and a MoO(y)(-) or MoO(y)(-2) moiety, and point to the relative stability of Mo=O versus Al=O bonds. The highest occupied and partially occupied orbitals in the anions and neutrals can be described as Mo atomic-like orbitals, so while the Mo is in a higher oxidation state than Al, the most energetically accessible electrons are localized on the molybdenum center.
Energy Technology Data Exchange (ETDEWEB)
Luna, C.R.; Germán, E.; Macchi, C. [IFIMAT, Universidad Nacional del Centro de la Provincia de Buenos Aires and CONICET, Pinto 399, B7000GHG Tandil (Argentina); Juan, A., E-mail: cajuan@uns.edu.ar [IFISUR, Dpto. Física, Universidad Nacional del Sur and CONICET, Av. Alem 1253, B8000 Bahía Blanca (Argentina); Somoza, A. [IFIMAT, Universidad Nacional del Centro de la Provincia de Buenos Aires and CICPBA, Pinto 399, B7000GHG Tandil (Argentina)
2013-04-15
Highlights: ► We study electronic and bonding properties of MgH{sub 2} systems containing vacancies. ► We examine two different transition metals as dopants, Nb and Zr atoms. ► We use ADF-DFT to compute the crystal orbital overlap population. ► We use VASP-DFT to compute binding energies and DOS. -- Abstract: The electronic and structural properties of MgH{sub 2} systems containing vacancies and Zr or Nb as dopants were studied using self-consistent calculations. The density of states were computed using the Vienna Ab initio Simulation Package (VASP) and the orbital overlap population weighted DOS with the Amsterdam Density Functional program. The metal–metal and metal–hydrogen bonds in the perfect hydride and this material containing a neutral Mg or H vacancies or a neutral mixed Mg–H vacancy complex were analyzed. The same calculations were also performed in the magnesium hydride with a Nb or a Zr atom as a substitutional impurity and on these systems containing the above mentioned vacancies. Simultaneously, the influence of vacancies in the hydride was studied through the calculation of the positron lifetimes and the positron–electron momentum distributions in the previously referred materials. Secondly, information on the influence of vacancies on the electron momentum density of the MgH{sub 2}(–Nb,–Zr) systems was additionally obtained through the calculation of the positron–electron momentum distributions. The results obtained indicate that in the pure hydride the presence of vacancies and impurities notable diminishes the force in the atomic bonds. The stability decrease of the bonds was correlated with changes in the positron wave function in the same sites of the structures. Moreover, it was found that these changes in the positron wave function are in good agreement with the decrease of the positron lifetimes.
Arockia Doss, M; Savithiri, S; Rajarajan, G; Thanikachalam, V; Anbuselvan, C
2015-12-05
FT-IR and FT-Raman spectra of 3-pentyl-2,6-di(furan-2-yl) piperidin-4-one (3-PFPO) were recorded in the solid phase. The structural and spectroscopic analyses of 3-PFPO were made by using B3LYP/HF level with 6-311++G(d, p) basis set. The fundamental vibrations are assigned on the basis of the total energy distribution (TED) of the vibrational modes, calculated with scaled quantum mechanics (SQM) method and PQS program. Comparison of the observed fundamental vibrational frequencies of 3-PFPO with calculated results by HF and DFT methods indicates that B3LYP is superior to HF method for molecular vibrational problems. The electronic properties such as excitation energies, oscillator strength, wavelengths and HOMO-LUMO energies were obtained by time-dependent DFT (TD-DFT) approach. The polarizability and first order hyperpolarizability of the title molecule were calculated and interpreted. The hyperconjugative interaction energy (E((2))) and electron densities of donor (i) and acceptor (j) bonds were calculated using NBO analysis. In addition, MEP and atomic charges of carbon, nitrogen, oxygen and hydrogen were calculated using B3LYP/6-311++G(d, p) level theory. Moreover, thermodynamic properties (heat capacities, entropy and enthalpy) of the title compound at different temperatures were calculated in gas phase.
Energy Technology Data Exchange (ETDEWEB)
Huang, Wenchao [National Laboratory for Infrared Physics, Shanghai Institute of Technical Physics, Chinese Academy of Sciences, Shanghai 200083 (China); Wang, Xiaofang, E-mail: wxiaof66@mail.sitp.ac.cn [National Laboratory for Infrared Physics, Shanghai Institute of Technical Physics, Chinese Academy of Sciences, Shanghai 200083 (China); Chen, Xiaoshuang, E-mail: xschen@mail.sitp.ac.cn [National Laboratory for Infrared Physics, Shanghai Institute of Technical Physics, Chinese Academy of Sciences, Shanghai 200083 (China); Lu, Wei [National Laboratory for Infrared Physics, Shanghai Institute of Technical Physics, Chinese Academy of Sciences, Shanghai 200083 (China); Damewood, L.; Fong, C.Y. [Department of Physics, University of California, Davis, CA 95616-8677 (United States)
2015-03-01
First principles calculations with spin polarization based on density functional theory have been performed on half-Heusler alloys PtXBi, with X=Mn, Fe, Co and Ni, in three different atomic configurations (i.e. α, β, and γ phases). For each configuration, their optimized lattice constants are determined. Electronic and magnetic properties are also investigated. The differences reflect the atomic arrangements of the three phases and varied transition metal elements X. Meanwhile, the possibility of having the integer magnetic moment for each phase is explored. PtMnBi in α phase show half-metallic (HM) properties when its lattice constant is reduced from −3.0% to −11.2% with magnetic moment consistent with the values given by the modified Slater–Pauling rule. Additionally, we examined the effects of the spin–orbit (S–O) interaction on half-metal PtMnBi by comparing the relative shifts of the valence bands and the indirect semiconducting gap with respect to the spin polarized results.
Huang, Wenchao; Wang, Xiaofang; Chen, Xiaoshuang; Lu, Wei; Damewood, L.; Fong, C. Y.
2015-03-01
First principles calculations with spin polarization based on density functional theory have been performed on half-Heusler alloys PtXBi, with X=Mn, Fe, Co and Ni, in three different atomic configurations (i.e. α, β, and γ phases). For each configuration, their optimized lattice constants are determined. Electronic and magnetic properties are also investigated. The differences reflect the atomic arrangements of the three phases and varied transition metal elements X. Meanwhile, the possibility of having the integer magnetic moment for each phase is explored. PtMnBi in α phase show half-metallic (HM) properties when its lattice constant is reduced from -3.0% to -11.2% with magnetic moment consistent with the values given by the modified Slater-Pauling rule. Additionally, we examined the effects of the spin-orbit (S-O) interaction on half-metal PtMnBi by comparing the relative shifts of the valence bands and the indirect semiconducting gap with respect to the spin polarized results.
Liu, Hong-Xia; Tang, Fu-Ling; Xue, Hong-Tao; Zhang, Yu; Cheng, Yu-Wen; Feng, Yu-Dong
2016-12-01
Using the first-principles plane-wave calculations within density functional theory, the perfect bi-layer and monolayer terminated WZ-CIS (100)/WZ-CdS (100) interfaces are investigated. After relaxation the atomic positions and the bond lengths change slightly on the two interfaces. The WZ-CIS/WZ-CdS interfaces can exist stably, when the interface bonding energies are -0.481 J/m2 (bi-layer terminated interface) and -0.677 J/m2 (monolayer terminated interface). Via analysis of the density of states, difference charge density and Bader charges, no interface state is found near the Fermi level. The stronger adhesion of the monolayer terminated interface is attributed to more electron transformations and orbital hybridizations, promoting stable interfacial bonds between atoms than those on a bi-layer terminated interface. Project supported by the National Natural Science Foundation of China (Grant Nos. 11164014 and 11364025) and the Gansu Science and Technology Pillar Program, China (Grant No. 1204GKCA057).
Calculation of electron wave functions and refractive index of Ne
Institute of Scientific and Technical Information of China (English)
2008-01-01
The radial wave functions of inner electron shell and outer electron shell of a Ne atom were obtained by the approximate analytical method and tested by calculating the ground state energy of the Ne atom. The equivalent volume of electron cloud and the refractive index of Ne were calculated. The calculated refractive index agrees well with the experimental result. Relationship between the refractive index and the wave function of Ne was discovered.
The electronic structures of solids
Coles, B R
2013-01-01
The Electronic Structures of Solids aims to provide students of solid state physics with the essential concepts they will need in considering properties of solids that depend on their electronic structures and idea of the electronic character of particular materials and groups of materials. The book first discusses the electronic structure of atoms, including hydrogen atom and many-electron atom. The text also underscores bonding between atoms and electrons in metals. Discussions focus on bonding energies and structures in the solid elements, eigenstates of free-electron gas, and electrical co
Institute of Scientific and Technical Information of China (English)
郑浩平; 吴丽华; 李根
2013-01-01
用第一性原理、全电子、从头计算方法构造了水溶液对缬氨酸(Val)电子结构的等效势.首先用自由团簇计算法得到能量最低时水分子与缬氨酸的相对空间位形,然后用团簇埋入自洽计算(SCCE)方法计算缬氨酸在水分子势下的电子结构,最后用偶极子势代替水分子势.结果表明:由于水溶液的存在,缬氨酸费米面下八个能级每个能级平均上升了约0.775 5 eV；水溶液对缬氨酸电子结构的影响可以很好地被偶极子势模拟.因此,所得的偶极子势可以直接运用到水溶液中蛋白质电子结构的计算中.%The equivalent potential of water for the electronic structure of valine (Val) was constructed on the basis of the first-principles, all-electron, ab initio calculations. The process involved three steps. First, a search for the minimum-energy configuration of the system Val + 7H2O was carried out by free cluster calculation. Then, the electronic structure of valine with the potential of water molecules was calculated with the self-consistent cluster-embedding (SCCE) method. Finally, the effect of water was simulated on valine by dipoles. Results show that the major effect of water on the electronic structure of valine is to raise the eigenvalues of eight orbitals under Fermi surface by about 0. 775 5 eV on average. The effect of water on the electronic structure of valine can be well simulated by dipoles. The equivalent potential obtained can be applied directly to the calculation of the electronic structures of proteins in solution.
Calculation of strange star structure
Directory of Open Access Journals (Sweden)
GH Bordbar
2009-12-01
Full Text Available In this paper, we have considered that the strange-star consists of quark matter from its center to surface. For quark matter, we have used two models, the MIT bag model and string-flip like model. In the bag model, the energy of the system has been considered the kinetic energy of the particles of system in addition to a constant B. We have considered two states for B, one of them is constant and the other one is density dependent. The second state has been obtained from the recent Cern data from quark-geleon plasma formation. In string-flip like model, the energy of the particles of the system has been obtained from the Schrodinger equation, where the Hamiltonian has been considered the sum of kinetic and potential energies. The potential in Hamiltonian is the general potential which depends on density that is the block potential. In the String-flip like model, the block potential is linear or square functions of the relative distance between two quarks. We have also obtained the equation of state of quark matter for all considered cases. Finally, we have computed the structure of the quark star using our equations of state.
Energy Technology Data Exchange (ETDEWEB)
Reboredo, F A; Hood, R Q; Kent, P C
2009-01-06
We develop a formalism and present an algorithm for optimization of the trial wave-function used in fixed-node diffusion quantum Monte Carlo (DMC) methods. The formalism is based on the DMC mixed estimator of the ground state probability density. We take advantage of a basic property of the walker configuration distribution generated in a DMC calculation, to (i) project-out a multi-determinant expansion of the fixed node ground state wave function and (ii) to define a cost function that relates the interacting-ground-state-fixed-node and the non-interacting trial wave functions. We show that (a) locally smoothing out the kink of the fixed-node ground-state wave function at the node generates a new trial wave function with better nodal structure and (b) we argue that the noise in the fixed-node wave function resulting from finite sampling plays a beneficial role, allowing the nodes to adjust towards the ones of the exact many-body ground state in a simulated annealing-like process. Based on these principles, we propose a method to improve both single determinant and multi-determinant expansions of the trial wave function. The method can be generalized to other wave function forms such as pfaffians. We test the method in a model system where benchmark configuration interaction calculations can be performed and most components of the Hamiltonian are evaluated analytically. Comparing the DMC calculations with the exact solutions, we find that the trial wave function is systematically improved. The overlap of the optimized trial wave function and the exact ground state converges to 100% even starting from wave functions orthogonal to the exact ground state. Similarly, the DMC total energy and density converges to the exact solutions for the model. In the optimization process we find an optimal non-interacting nodal potential of density-functional-like form whose existence was predicted in a previous publication [Phys. Rev. B 77 245110 (2008)]. Tests of the method are
Correlated Electron Calculations with Hartree-Fock Scaling
Gebauer, Ralph; Car, Roberto
2013-01-01
We introduce an energy functional for ground-state electronic structure calculations with fundamental variables the natural spin orbitals and their joint occupation probabilities in an implied many-body trial wave function. We use a controlled approximation for the two-particle density matrix that greatly extends the accuracy compared to current functionals of the one-particle density matrix only. Algebraic scaling of computational cost with electron number is achieved in general, and Hartree-Fock scaling in the seniority-zero version of the theory. We present results obtained with the latter version for saturated small molecular systems for which highly accurate quantum chemical computations are available for comparison. The results are variational, capturing most of the correlation energy from equilibrium to dissociation.
Electronic structure of sulfanilamides
Energy Technology Data Exchange (ETDEWEB)
Grechishkin, V.S.; Grechishkina, R.V.; Starovoitova, O.V.
1986-05-01
At present, about 30,000 derivatives of sulfanilamide are known. The establishment of a relationship between the structure of these compounds and their bacteriostatic activity is an urgent problem. In the present work, this problem is solved by means of NQR and NMR spectroscopy. Since the content of the /sup 14/N nuclei in these molecules is not high, to run the NQR, they used the double resonance method. Some samples of the sulfanilamides were studied by direct pulsed NQR method. The high resolution NMR spectra were run in heavy water solution on a RS-60MA spectrometer. All the measurements were carried out at 120/sup 0/K in the solid phase. The results of the calculation of eQq/sub zz/ for the NH/sub 2/ groups in the sulfanilamide residue are listed. To interpret the results by the MO LCAO method in the Hueckel approximation on the EC-1022 computer by a special FORTRAN program, they calculated the charged rho on an atom in the amino group with parameters of hetero atoms and coupling constants.
Atomic Structure Calculations for Neutral Oxygen
Norah Alonizan; Rabia Qindeel; Nabil Ben Nessib
2016-01-01
Energy levels and oscillator strengths for neutral oxygen have been calculated using the Cowan (CW), SUPERSTRUCTURE (SS), and AUTOSTRUCTURE (AS) atomic structure codes. The results obtained with these atomic codes have been compared with MCHF calculations and experimental values from the National Institute of Standards and Technology (NIST) database.
Electronic structure and tautomerism of thioamides
Energy Technology Data Exchange (ETDEWEB)
Novak, Igor, E-mail: inovak@csu.edu.au [Charles Sturt University, POB 883, Orange, NSW 2800 (Australia); Klasinc, Leo, E-mail: klasinc@irb.hr [Physical Chemistry Department, Ruđer Bošković Institute, HR-10002 Zagreb (Croatia); McGlynn, Sean P., E-mail: sean.mcglynn@chemgate.chem.lsu.edu [Louisiana State University, Baton Rouge, LA 70803 (United States)
2016-05-15
Highlights: • Electronic structure of thioamide group and its relation to Lewis basicity. • Tautomerism of the (thio)amide groups. • Substituent effects on the electronic structure of (thio)amide group. - Abstract: The electronic structures of several thioamides have been studied by UV photoelectron spectroscopy (UPS). The relative stabilities of keto–enol tautomers have been determined using high-level ab initio calculations and the results were used in the analysis of UPS spectra. The main features of electronic structure and tautomerism of thioamide derivatives are discussed. The predominant tautomers in the gas phase are of keto–(thio)keto form. The addition of cyclohexanone moiety to the thioamide group enhances the Lewis base character of the sulfur atom. The addition of phenyl group to the (thio)amide group significantly affects its electronic structure.
2015-04-01
distribution is unlimited. i CONTENTS Page Introduction 1 Two-dimensional Material Geometry and Analogs with Close-packed Systems 1 Matching...distribution is unlimited. 1 INTRODUCTION Two-dimensional (2D) material heterostructures offer novel and compelling electronic and optical...methods have undoubtedly been created for matching lattice constants of dissimilar nanomaterials , very few are actually covered explicitly in literature
Electronic structure of spin systems
Energy Technology Data Exchange (ETDEWEB)
Saha-Dasgupta, Tanusri
2016-04-15
Highlights: • We review the theoretical modeling of quantum spin systems. • We apply the Nth order muffin-tin orbital electronic structure method. • The method shows the importance of chemistry in the modeling. • CuTe{sub 2}O{sub 5} showed a 2-dimensional coupled spin dimer behavior. • Ti substituted Zn{sub 2}VO(PO{sub 4}){sub 2} showed spin gap behavior. - Abstract: Low-dimensional quantum spin systems, characterized by their unconventional magnetic properties, have attracted much attention. Synthesis of materials appropriate to various classes within these systems has made this field very attractive and a site of many activities. The experimental results like susceptibility data are fitted with the theoretical model to derive the underlying spin Hamiltonian. However, often such a fitting procedure which requires correct guess of the assumed spin Hamiltonian leads to ambiguity in deciding the representative model. In this review article, we will describe how electronic structure calculation within the framework of Nth order muffin-tin orbital (NMTO) based Wannier function technique can be utilized to identify the underlying spin model for a large number of such compounds. We will show examples from compounds belonging to vanadates and cuprates.
Energy Technology Data Exchange (ETDEWEB)
Choi, Sukgeun [National Renewable Energy Lab. (NREL), Golden, CO (United States); Park, Ji-Sang [National Renewable Energy Lab. (NREL), Golden, CO (United States); Donohue, Andrea [J. A. Woollam Co. Inc., Lincoln, NE (United States); Christensen, Steven T. [National Renewable Energy Lab. (NREL), Golden, CO (United States); To, Bobby [National Renewable Energy Lab. (NREL), Golden, CO (United States); Beall, Carolyn [National Renewable Energy Lab. (NREL), Golden, CO (United States); Wei, Su-Huai [National Renewable Energy Lab. (NREL), Golden, CO (United States); Repins, Ingid L. [National Renewable Energy Lab. (NREL), Golden, CO (United States)
2015-11-19
Cu_{2}ZnGeSe_{4} is of interest for the development of next-generation thin-film photovoltaic technologies. To understand its electronic structure and related fundamental optical properties, we perform first-principles calculations for three structural variations: kesterite, stannite, and primitive-mixed CuAu phases. The calculated data are compared with the room-temperature dielectric functionϵ=ϵ1+iϵ2 spectrum of polycrystalline Cu_{2}ZnGeSe_{4} determined by vacuum-ultraviolet spectroscopic ellipsometry in the photon-energy range of 0.7 to 9.0 eV. Ellipsometric data are modeled with the sum of eight Tauc-Lorentz oscillators, and the best-fit model yields the band-gap and Tauc-gap energies of 1.25 and 1.19 eV, respectively. A comparison of overall peak shapes and relative intensities between experimental spectra and the calculated ϵ data for three structural variations suggests that the sample may not have a pure (ordered) kesterite phase. We found that the complex refractive index N=n+ik, normal-incidence reflectivity R, and absorption coefficients α are calculated from the modeled ϵ spectrum, which are also compared with those of Cu_{2}ZnSnSe_{4} . The spectral features for Cu_{2}ZnGeSe_{4} appear to be weaker and broader than those for Cu_{2}ZnSnSe_{4} , which is possibly due to more structural imperfections presented in Cu_{2}ZnGeSe_{4} than Cu_{2}ZnSnSe_{4} .
Zhao, Zong-Yan; Liu, Qing-Lu; Dai, Wen-Wu
2016-08-23
Six BiOX1-xYx (X, Y = F, Cl, Br, and I) solid solutions have been systematically investigated by density functional theory calculations. BiOCl1-xBrx, BiOBr1-xIx, and BiOCl1-xIx solid solutions have very small bowing parameters; as such, some of their properties increase almost linearly with increasing x. For BiOF1-xYx solid solutions, the bowing parameters are very large and it is extremely difficult to fit the related calculated data by a single equation. Consequently, BiOX1-xYx (X, Y = Cl, Br, and I) solid solutions are highly miscible, while BiOF1-xYx (Y = Cl, Br, and I) solid solutions are partially miscible. In other words, BiOF1-xYx solid solutions have miscibility gaps or high miscibility temperature, resulting in phase separation and F/Y inhomogeneity. Comparison and analysis of the calculated results and the related physical-chemical properties with different halogen compositions indicates that the parameters of BiOX1-xYx solid solutions are determined by the differences of the physical-chemical properties of the two halogen compositions. In this way, the large deviation of some BiOX1-xYx solid solutions from Vegard's law observed in experiments can be explained. Moreover, the composition ratio of BiOX1-xYx solid solutions can be measured or monitored using optical measurements.
Energy Technology Data Exchange (ETDEWEB)
Abdiche, A., E-mail: abdiche_a@yahoo.fr [Engineering Physics Laboratory, Tiaret University, 14000 Tiaret (Algeria); Baghdad, R. [Engineering Physics Laboratory, Tiaret University, 14000 Tiaret (Algeria); Khenata, R., E-mail: khenata_rabah@yahoo.fr [Laboratoire de Physique Quantique et de Modelisation Mathematique (LPQ3M), Departement de Technologie, Universite de Mascara, 29000 Mascara (Algeria); Department of Physics and Astronomy, King Saud University, P.O Box 2455, Riyadh 11451 (Saudi Arabia); Riane, R. [Computational Materials Science Laboratory, University Research of Sidi-Bel-Abbes, 22000 Algeria (Algeria); Al-Douri, Y. [Institute of Nono Electronic Engineering, University Malaysia Perlis, 01000 Kangar, Perlis (Malaysia); Guemou, M. [Engineering Physics Laboratory, Tiaret University, 14000 Tiaret (Algeria); Bin-Omran, S. [Department of Physics and Astronomy, King Saud University, P.O Box 2455, Riyadh 11451 (Saudi Arabia)
2012-02-01
The structural and electronic properties of cubic zinc blende BN, BP, AlN and AlP compounds and their B{sub x}Al{sub 1-x}N{sub y}P{sub 1-y} quaternary alloys, have been calculated using the non relativistic full-potential linearized-augmented plane wave FP-LAPW method. The exchange-correlation potential is treated with the local density approximation of Perdew and Wang (LDA-PW) as well as the generalized gradient approximation (GGA) of Perdew-Burke and Ernzerhof (GGA-PBE). The calculated structural properties of BN, BP, AlN and AlP compounds are in good agreement with the available experimental and theoretical data. A nonlinear variation of compositions x and y with the lattice constants, bulk modulus, direct and indirect band gaps is found. The calculated bowing of the fundamental band gaps is in good agreement with the available experimental and theoretical value. To our knowledge this is the first quantitative theoretical investigation on B{sub x}Al{sub 1-x}N{sub y}P{sub 1-y} quaternary alloy and still awaits experimental confirmations.
Energy Technology Data Exchange (ETDEWEB)
Amari, S., E-mail: siham_amari@yahoo.fr [Laboratoire de Modelisation et de Simulation en Sciences des Materiaux, Departement de Physique Universite Djillali Liabes, Sidi Bel-Abbes (Algeria); Mecabih, S.; Abbar, B.; Bouhafs, B. [Laboratoire de Modelisation et de Simulation en Sciences des Materiaux, Departement de Physique Universite Djillali Liabes, Sidi Bel-Abbes (Algeria)
2012-09-15
In this work, we aim to examine the spin-polarized electronic band structures, the local densities of states as well as the magnetism of Zn{sub 1-x}TM{sub x}Se (TM=Cr, Fe, Co and Ni) diluted magnetic semiconductors in the ferromagnetic (FM) and antiferromagnetic (AFM) phases, and with 25% of TM. The calculations are performed by the developed full-potential augmented plane wave plus local orbitals method within the spin density functional theory. As exchange-correlation potential we used the generalized gradient approximation (GGA) form. We treated the ferromagnetic and antiferromagnetic phases and we found that all compounds are stable in the ferromagnetic structure. Structural properties are computed after total energy minimization. Our results show that the cohesive energies of Zn{sub 0.75}TM{sub 0.25}Se are greater than that of zinc blende ZnSe. We discuss the electronic structures, total and partial densities of states, local moments and the p-d exchange splitting. Furthermore, we found that p-d hybridization reduces the local magnetic moment of TM and produces small local magnetic moments on the nonmagnetic Zn and Se sites. We found also that in the AFM phase the TM local magnetic moments are smaller than in the FM phase; this is due to the greater interaction of the TM d-up and d-down orbitals. - Highlights: Black-Right-Pointing-Pointer The calculation of the exchange constants of ZnTMSe (TM=Cr, Fe, Co and Ni). Black-Right-Pointing-Pointer Prediction of the spin-exchange splitting of ZnTMSe (TM=Cr, Fe, Co and Ni). Black-Right-Pointing-Pointer The study of ZnTMSe diluted magnetic semiconductors in the FM and AFM phases.
Electronic structure interpolation via atomic orbitals.
Chen, Mohan; Guo, G-C; He, Lixin
2011-08-17
We present an efficient scheme for accurate electronic structure interpolation based on systematically improvable optimized atomic orbitals. The atomic orbitals are generated by minimizing the spillage value between the atomic basis calculations and the converged plane wave basis calculations on some coarse k-point grid. They are then used to calculate the band structure of the full Brillouin zone using the linear combination of atomic orbitals algorithms. We find that usually 16-25 orbitals per atom can give an accuracy of about 10 meV compared to the full ab initio calculations, and the accuracy can be systematically improved by using more atomic orbitals. The scheme is easy to implement and robust, and works equally well for metallic systems and systems with complicated band structures. Furthermore, the atomic orbitals have much better transferability than Shirley's basis and Wannier functions, which is very useful for perturbation calculations.
An electronic structure perspective of graphene interfaces
Schultz, Brian J.; Dennis, Robert V.; Lee, Vincent; Banerjee, Sarbajit
2014-03-01
The unusual electronic structure of graphene characterized by linear energy dispersion of bands adjacent to the Fermi level underpins its remarkable transport properties. However, for practical device integration, graphene will need to be interfaced with other materials: 2D layered structures, metals (as ad-atoms, nanoparticles, extended surfaces, and patterned metamaterial geometries), dielectrics, organics, or hybrid structures that in turn are constituted from various inorganic or organic components. The structural complexity at these nanoscale interfaces holds much promise for manifestation of novel emergent phenomena and provides a means to modulate the electronic structure of graphene. In this feature article, we review the modifications to the electronic structure of graphene induced upon interfacing with disparate types of materials with an emphasis on iterative learnings from theoretical calculations and electronic spectroscopy (X-ray absorption fine structure (XAFS) spectroscopy, scanning transmission X-ray microscopy (STXM), angle-resolved photoemission spectroscopy (ARPES), and X-ray magnetic circular dichroism (XMCD)). We discuss approaches for engineering and modulating a bandgap in graphene through interfacial hybridization, outline experimental methods for examining electronic structure at interfaces, and overview device implications of engineered interfaces. A unified view of how geometric and electronic structure are correlated at interfaces will provide a rational means for designing heterostructures exhibiting emergent physical phenomena with implications for plasmonics, photonics, spintronics, and engineered polymer and metal matrix composites.
Directory of Open Access Journals (Sweden)
Juan Carlos Salcedo-Reyes
2008-09-01
Full Text Available Usually, semiconductor ternary alloys are studied via a pseudo-binary approach in which the semiconductoris described like a crystalline array were the cation/anion sub-lattice consist of a random distribution of thecationic/anionic atoms. However, in the case of reported III-V and II-VI artificial structures, in which anordering of either the cations or the anions of the respective fcc sub-lattice is involved, a pseudo-binaryapproach can no longer be employed, an atomistic point of view, which takes into account the localstructure, must be used to study the electronic and optical properties of these artificial semiconductoralloys. In particular, the ordered Zn0.5Cd0.5Se alloy has to be described as a crystal with the simple-tetragonalBravais lattice with a composition equal to the zincblende random ternary alloy. The change of symmetryproperties of the tetragonal alloy, in relation to the cubic alloy, results mainly in two effects: i reduction ofthe banned gap, and ii crystal field cleavage of the valence band maximum. In this work, the electronicband structure of the ordered Zn0.5Cd0.5Se alloy is calculated using a second nearest neighbor semi-empiricaltight binding method. Also, it is compared with the electronic band structure obtained by FP-LAPW (fullpotentiallinearized augmented-plane wave method.
Indian Academy of Sciences (India)
P Modak; R S Rao; B K Godwal; S K Sikka
2002-05-01
Results of ab initio electronic structure calculations on the compound MgB2 using the FPLAPW method employing GGA for the exchange-correlation energy are presented. Total energy minimization enables us to estimate the equilibrium volume, / ratio and the bulk modulus, all of which are in excellent agreement with experiment. We obtain the mass enhancement parameter by using our calculated (F) and the experimental speciﬁc heat data. The c is found to be 24.7 K.
The electronic structure of antiferromagnetic chromium
DEFF Research Database (Denmark)
Skriver, Hans Lomholt
1981-01-01
The author has used the local spin density formalism to perform self-consistent calculations of the electronic structure of chromium in the non-magnetic and commensurate antiferromagnetic phases, as a function of the lattice parameter. A change of a few per cent in the atomic radius brings...
The Electronic Structure Effect in Heterogeneous Catalysis
DEFF Research Database (Denmark)
Nilsson, A.; Pettersson, L. G. M.; Hammer, Bjørk
2005-01-01
Using a combination of density functional theory calculations and X-ray emission and absorption spectroscopy for nitrogen on Cu and Ni surfaces, a detailed picture is given of the chemisorption bond. It is suggested that the adsorption bond strength and hence the activity of transition metal...... surfaces as catalysts for chemical reactions can be related to certain characteristics of the surface electronic structure....
Beccaceci, Sonya; Armata, Nerina; Ogden, J Steven; Dyke, John M; Rhyman, Lydia; Ramasami, Ponnadurai
2012-02-21
The reactions of dimethylsulfide (DMS) with molecular iodine (I(2)) and iodine monochloride (ICl) have been studied by infrared matrix isolation spectroscopy by co-condensation of the reagents in an inert gas matrix. Molecular adducts of DMS + I(2) and DMS + ICl have also been prepared using standard synthetic methods. The vapour above each of these adducts trapped in an inert gas matrix gave the same infrared spectrum as that recorded for the corresponding co-condensation reaction. In each case, the infrared spectrum has been interpreted in terms of a van der Waals adduct, DMS : I(2) and DMS : ICl, with the aid of infrared spectra computed for their minimum energy structures at the MP2 level. Computed relative energies of minima and transition states on the potential energy surfaces of these reactions were used to understand why they do not proceed further than the reactant complexes DMS : I(2) and DMS : ICl. The main findings of this research are compared with results obtained earlier for the DMS + Cl(2) and DMS + Br(2) reactions, and the atmospheric implications of the conclusions are also considered.
DEFF Research Database (Denmark)
Lu, Jing Tao; Christensen, Rasmus Bjerregaard; Foti, Giuseppe;
2014-01-01
We extend the simple and efficient lowest order expansion (LOE) for inelastic electron tunneling spectroscopy (IETS) to include variations in the electronic structure on the scale of the vibration energies. This enables first-principles calculations of IETS line shapes for molecular junctions clo...
Jong, Un-Gi; Yu, Chol-Jun; Ri, Jin-Song; Kim, Nam-Hyok; Ri, Guk-Chol
2016-09-01
Extensive studies have demonstrated the promising capability of the organic-inorganic hybrid halide perovskite CH3NH3PbI3 in solar cells with a high power conversion efficiency exceeding 20%. However, the intrinsic as well as extrinsic instabilities of this material remain the major challenge to the commercialization of perovskite-based solar cells. Mixing halides is expected to resolve this problem. Here, we investigate the effect of chemical substitution in the position of the halogen atom on the structural, electronic, and optical properties of mixed halide perovskites CH3NH3Pb (I1-xBrx) 3 with a pseudocubic phase using the virtual crystal approximation method within density functional theory. With an increase of Br content x from 0.0 to 1.0, the lattice constant decreases in proportion to x with the function of a (x )=6.420 -0.333 x (Å), while the band gap and the exciton binding energy increase with the quadratic function of Eg(x ) =1.542 +0.374 x +0.185 x2 (eV) and the linear function of Eb(x ) =0.045 +0.057 x (eV), respectively. The photoabsorption coefficients are also calculated, showing a blueshift of the absorption onsets for higher Br contents. We calculate the phase decomposition energy of these materials and analyze the electronic charge density difference to estimate the material stability. Based on the calculated results, we suggest that the best match between efficiency and stability can be achieved at x ≈0.2 in CH3NH3Pb (I1-xBrx) 3 perovskites.
Fujisawa, Jun-ichi; Hanaya, Minoru
2016-06-01
Interfacial charge-transfer (ICT) transitions between inorganic semiconductors and π-conjugated molecules allow direct charge separation without loss of energy. This feature is potentially useful for efficient photovoltaic conversions. Charge-transferred complexes of TiO2 nanoparticles with 7,7,8,8-tetracyanoquinodimethane (TCNQ) and its analogues (TCNX) show strong ICT absorption in the visible region. The ICT band was reported to be significantly red-shifted with extension of the π-conjugated system of TCNX. In order to clarify the mechanism of the red-shift, in this work, we systematically study electronic structures of the TiO2-TCNX surface complexes (TCNX; TCNE, TCNQ, 2,6-TCNAQ) by ionization potential measurements and density functional theory (DFT) calculations.
Multiconfiguration calculations of electronic isotope shift factors in Al I
Filippin, Livio; Ekman, Jörgen; Fritzsche, Stephan; Godefroid, Michel; Jönsson, Per
2016-01-01
The present work reports results from systematic multiconfiguration Dirac-Hartree-Fock calculations of electronic isotope shift factors for a set of transitions between low-lying states in neutral aluminium. These electronic quantities together with observed isotope shifts between different pairs of isotopes provide the changes in mean-square charge radii of the atomic nuclei. Two computational approaches are adopted for the estimation of the mass- and field shift factors. Within these approaches, different models for electron correlation are explored in a systematic way to determine a reliable computational strategy and estimate theoretical uncertainties of the isotope shift factors.
Calculation of band structure in (101)-biaxially strained Si
Institute of Scientific and Technical Information of China (English)
无
2009-01-01
The structure model used for calculation was defined according to Vegard’s rule and Hooke’s law. Calculations were performed on the electronic structures of(101)-biaxially strained Si on relaxed Si1-X GeX alloy with Ge fraction ranging from X = 0 to 0.4 in steps of 0.1 by CASTEP approach. It was found that [±100] and [00±1] valleys(-4) splitting from the [0±10] valley(-2) constitute the conduction b0and(CB) edge,that valence band(VB) edge degeneracy is partially lifted and that the electron mass is un-altered under strain while the hole mass decreases in the [100] and [010] directions. In addition,the fitted dependences of CB splitting energy,VB splitting energy and indirect bandgap on X are all linear.
Cobalamins uncovered by modern electronic structure calculations
DEFF Research Database (Denmark)
Kepp, Kasper Planeta; Ryde, Ulf
2009-01-01
This review describes how computational methods have contributed to the held of cobalamin chemistry since the start of the new millennium. Cobalamins are cobalt-dependent cofactors that are used for alkyl transfer and radical initiation by several classes of enzymes. Since the entry of modern...
Directory of Open Access Journals (Sweden)
Haipeng Lu
2016-03-01
Full Text Available Employing first-principles calculations, structural, electronic properties of new multiferroic material Er2NiMnO6/La2NiMnO6 perovskite superlattice are investigated. This structure is computed as monoclinic phase with obvious distortion. The average in-plane anti-phase rotation angle, average out-of-plane in-phase rotation angle and other microscopic features are reported in this paper. Ni and Mn are found in this superlattice that stay high spin states. These microscopic properties play important roles in multiferroic properties. Based on these microscopic features, the relationship between the direction of spontaneous polarization and the order of substitution in neighboring A-O layers is explained. Finally, we try to enhance the electrical polarization magnitude by 32% by altering the previous superlattice as LaEr2NiMnO7 structure. Our results show that both repulsion force of A site rare earth ions and the arrangement of B site ions can exert influences on spontaneous polarization.
Electronic Properties in a Hierarchical Multilayer Structure
Institute of Scientific and Technical Information of China (English)
ZHU Chen-Ping; XIONG Shi-Jie
2001-01-01
We investigate electronic properties of a hierarchical multilayer structure consisting of stacking of barriers and wells. The structure is formed in a sequence of generations, each of which is constructed with the same pattern but with the previous generation as the basic building blocks. We calculate the transmission spectrum which shows the multifractal behavior for systems with large generation index. From the analysis of the average resistivity and the multifractal structure of the wavefunctions, we show that there exist different types of states exhibiting extended, localized and intermediate characteristics. The degree of localization is sensitive to the variation of the structural parameters.Suggestion of the possible experimental realization is discussed.
Energy Technology Data Exchange (ETDEWEB)
Lavrentyev, A.A.; Gabrelian, B.V.; Vorzhev, V.B.; Nikiforov, I.Ya. [Department of Physics, Don State Technical University, Gagarin Sq. 1, Rostov-on-Don (Russian Federation); Khyzhun, O.Yu. [Frantsevych Institute for Problems of Materials Science, National Academy of Sciences of Ukraine, 3 Krzhyzhanivsky Street, UA-03142 Kyiv (Ukraine)], E-mail: khyzhun@ipms.kiev.ua
2009-03-20
To investigate the influence of substitution of carbon atoms for nitrogen atoms in the cubic TaC{sub x}N{sub 1-x} carbonitrides, total and partial densities of states were calculated for TaC, TaC{sub 0.5}N{sub 0.5} and TaN compounds (NaCl structure) using the self-consistent cluster (with the FEFF8 code) and ab initio band-structure augmented plane wave + local orbitals (APW + LO) methods. In the present work a rather good agreement of the theoretical FEFF8 and APW + LO data for electronic properties of the TaC{sub x}N{sub 1-x} system under consideration was obtained. The results indicate that a strong hybridization of the Ta 5d- and C(N) 2p-like states is characteristic for the valence band of the TaC{sub x}N{sub 1-x} carbonitrides. When going from TaC to TaN through the TaC{sub 0.5}N{sub 0.5} carbonitride, the main maxima of curves representing total and partial Ta 5d densities of states shift in the direction opposite to the position of the Fermi level. In the above sequence of compounds, an increase of occupation of the near-Fermi sub-band formed by contributions of Ta 5d(t{sub 2g}) states has been detected. The theoretical FEFF8 and APW + LO results for the electronic structure of the TaC{sub x}N{sub 1-x} carbonitrides were found to be in excellent agreement with the experimental data derived in the present work employing X-ray photoelectron, emission and absorption spectroscopy methods for cubic TaC{sub 0.98}, TaC{sub 0.52}N{sub 0.49} and TaN{sub 0.97} compounds.
Duan, Yuhua; Lekse, Jonathan; Wang, Xianfeng; Li, Bingyun; Alcántar-Vázquez, Brenda; Pfeiffer, Heriberto; Halley, J. W.
2015-04-01
The electronic structural and phonon properties of Na2 -αMαZr O3 (M =Li ,K, α =0.0 ,0.5,1.0,1.5,2.0) are investigated by first-principles density-functional theory and phonon dynamics. The thermodynamic properties of CO2 absorption and desorption in these materials are also analyzed. With increasing doping level α , the binding energies of Na2 -αLiαZr O3 are increased while the binding energies of Na2 -αKαZrO3 are decreased to destabilize the structures. The calculated band structures and density of states also show that, at the same doping level, the doping sites play a significant role in the electronic properties. The phonon dispersion results show that few soft modes are found in several doped configurations, which indicates that these structures are less stable than other configurations with different doping levels. From the calculated relationships among the chemical-potential change, the CO2 pressure, and the temperature of the CO2 capture reactions by Na2 -αMαZr O3 , and from thermogravimetric-analysis experimental measurements, the Li- and K-doped mixtures Na2 -αMαZr O3 have lower turnover temperatures (Tt ) and higher CO2 capture capacities, compared to pure Na2Zr O3 . The Li-doped systems have a larger Tt decrease than the K-doped systems. When increasing the Li-doping level α , the Tt of the corresponding mixture Na2 -αLiαZr O3 decreases further to a low-temperature range. However, in the case of K-doped systems Na2 -αKαZr O3 , although doping K into Na2Zr O3 initially shifts its Tt to lower temperatures, further increases of the K-doping level α causes Tt to increase. Therefore, doping Li into Na2Zr O3 has a larger influence on its CO2 capture performance than the K-doped Na2Zr O3 . Compared with pure solids M2Zr O3 , after doping with other elements, these doped systems' CO2 capture performances are improved.
Electron impact double ionization of helium from classical trajectory calculations
Geyer, T
2004-01-01
With a recently proposed quasiclassical ansatz [Geyer and Rost, J. Phys. B 35 (2002) 1479] it is possible to perform classical trajectory ionization calculations on many electron targets. The autoionization of the target is prevented by a M\\o{}ller type backward--forward propagation scheme and allows to consider all interactions between all particles without additional stabilization. The application of the quasiclassical ansatz for helium targets is explained and total and partially differential cross sections for electron impact double ionization are calculated. In the high energy regime the classical description fails to describe the dominant TS1 process, which leads to big deviations, whereas for low energies the total cross section is reproduced well. Differential cross sections calculated at 250 eV await their experimental confirmation.
Slebarski, A.; Orzechowska, M.; Wrona, A.; Szade, J.; Jezierski, A.
2000-02-01
We report on structural measurements on and electronic structure investigations of the alloyed compounds ZrNiSn, TiNiSn, CeNiSn and CeRhSb. We present measurements of lattice parameters as a function of temperature and analysis of a (T ) and its relation to icons/Journals/Common/chi" ALT="chi" ALIGN="TOP"/> T , icons/Journals/Common/chi" ALT="chi" ALIGN="TOP"/> being the magnetic susceptibility. We observed a linear dependence of a (T ) versus icons/Journals/Common/chi" ALT="chi" ALIGN="TOP"/> T for Zr, Ti and Ce alloys (for orthorhombic Ce alloys, the lattice parameters a , b and c scale linearly with icons/Journals/Common/chi" ALT="chi" ALIGN="TOP"/> T ). The x-ray photoelectron and ultraviolet photoemission spectra are further compared to the density of states, obtained from band-structure calculations.
Lattice QCD Calculation of Nucleon Structure
Energy Technology Data Exchange (ETDEWEB)
Liu, Keh-Fei [University of Kentucky, Lexington, KY (United States). Dept. of Physics and Astronomy; Draper, Terrence [University of Kentucky, Lexington, KY (United States). Dept. of Physics and Astronomy
2016-08-30
It is emphasized in the 2015 NSAC Long Range Plan that "understanding the structure of hadrons in terms of QCD's quarks and gluons is one of the central goals of modern nuclear physics." Over the last three decades, lattice QCD has developed into a powerful tool for ab initio calculations of strong-interaction physics. Up until now, it is the only theoretical approach to solving QCD with controlled statistical and systematic errors. Since 1985, we have proposed and carried out first-principles calculations of nucleon structure and hadron spectroscopy using lattice QCD which entails both algorithmic development and large-scale computer simulation. We started out by calculating the nucleon form factors -- electromagnetic, axial-vector, πNN, and scalar form factors, the quark spin contribution to the proton spin, the strangeness magnetic moment, the quark orbital angular momentum, the quark momentum fraction, and the quark and glue decomposition of the proton momentum and angular momentum. The first round of calculations were done with Wilson fermions in the `quenched' approximation where the dynamical effects of the quarks in the sea are not taken into account in the Monte Carlo simulation to generate the background gauge configurations. Beginning in 2000, we have started implementing the overlap fermion formulation into the spectroscopy and structure calculations. This is mainly because the overlap fermion honors chiral symmetry as in the continuum. It is going to be more and more important to take the symmetry into account as the simulations move closer to the physical point where the u and d quark masses are as light as a few MeV only. We began with lattices which have quark masses in the sea corresponding to a pion mass at ~ 300 MeV and obtained the strange form factors, charm and strange quark masses, the charmonium spectrum and the D_{s} meson decay constant f_{Ds}, the strangeness and charmness, the meson mass
Lattice QCD Calculation of Nucleon Structure
Energy Technology Data Exchange (ETDEWEB)
Liu, Keh-Fei; Draper, Terrence
2016-08-30
It is emphasized in the 2015 NSAC Long Range Plan [1] that \\understanding the structure of hadrons in terms of QCD's quarks and gluons is one of the central goals of modern nuclear physics." Over the last three decades, lattice QCD has developed into a powerful tool for ab initio calculations of strong-interaction physics. Up until now, it is the only theoretical approach to solving QCD with controlled statistical and systematic errors. Since 1985, we have proposed and carried out rst-principles calculations of nucleon structure and hadron spectroscopy using lattice QCD which entails both algorithmic development and large scale computer simulation. We started out by calculating the nucleon form factors { electromagnetic [2], axial-vector [3], NN [4], and scalar [5] form factors, the quark spin contribution [6] to the proton spin, the strangeness magnetic moment [7], the quark orbital angular momentum [8], the quark momentum fraction [9], and the quark and glue decomposition of the proton momentum and angular momentum [10]. These rst round of calculations were done with Wilson fermions in the `quenched' approximation where the dynamical e ects of the quarks in the sea are not taken into account in the Monte Carlo simulation to generate the background gauge con gurations. Beginning in 2000, we have started implementing the overlap fermion formulation into the spectroscopy and structure calculations [11, 12]. This is mainly because the overlap fermion honors chiral symmetry as in the continuum. It is going to be more and more important to take the symmetry into account as the simulations move closer to the physical point where the u and d quark masses are as light as a few MeV only. We began with lattices which have quark masses in the sea corresponding to a pion mass at 300 MeV and obtained the strange form factors [13], charm and strange quark masses, the charmonium spectrum and the Ds meson decay constant fDs [14], the strangeness and charmness [15], the
Energy Technology Data Exchange (ETDEWEB)
Tholomier, M.; Vicario, E.; Doghmane, N.
1987-10-01
The contribution of backscattered electrons to Auger electrons yield was studied with a multiple scattering Monte-Carlo simulation. The Auger backscattering factor has been calculated in the 5 keV-60 keV energy range. The dependence of the Auger backscattering factor on the primary energy and the beam incidence angle were determined. Spatial distributions of backscattered electrons and Auger electrons are presented for a point incident beam. Correlations between these distributions are briefly investigated.
Vogt, Natalja; Khaikin, Leonid S; Grikina, Olga E; Rykov, Anatolii N; Vogt, Jürgen
2008-08-21
Thymine is one of the nucleobases which forms the nucleic acid (NA) base pair with adenine in DNA. The study of molecular structure and dynamics of nucleobases can help to understand and explain some processes in biological systems and therefore it is of interest. Because the scattered intensities on the C, N, and O atoms as well as some bond lengths in thymine are close to each other the structural problem cannot been solved by the gas phase electron diffraction (GED) method alone. Therefore the rotational constants from microvawe (MW) studies and differences in the groups of N-C, C=O, N-H, and C-H bond lengths from MP2 (full)/cc-pVQZ calculations were used as supplementary data. The analysis of GED data was based on the C(s) molecular symmetry according to results of the structure optimizations at the MP2 (full) level using 6-311G (d,p), cc-pVTZ, and cc-pVQZ basis sets confirmed by vibrational frequency calculations with 6-311G (d,p) and cc-pVTZ basis sets. Mean-square amplitudes as well as harmonic and anharmonic vibrational corrections to the internuclear distances (r(e)-r(a)) and to the rotational constants (B(e)(k)-B(0)(k), where k = A, B, C) were calculated from the quadratic (MP2 (full)/cc-pVTZ) and cubic (MP2 (full)/6-311G (d,p)) force constants (the latter were used only for anharmonic corrections). The harmonic force field was scaled using published IR and Raman spectra of the parent and N1,N3-dideuterated species, which were for the first time completely assigned in the present work. The main equilibrium structural parameters of the thymine molecule determined from GED data supplemented by MW rotational constants and results of MP2 calculations are the following (bond lengths in Angstroms and bond angles in degrees with 3sigma in parentheses): r(e) (C5=C6) = 1.344 (16), r(e) (C5-C9) = 1.487 (8), r(e) (N1-C6) = 1.372 (3), r(e) (N1-C2) = 1.377 (3), r(e) (C2-N3) = 1.378 (3), r(e) (N3-C4) = 1.395 (3), r(e) (C2=O7) = 1.210 (1), r(e) (C4=O8) = 1.215 (1
Intensity modulation with electrons: calculations, measurements and clinical applications.
Karlsson, M G; Karlsson, M; Zackrisson, B
1998-05-01
Intensity modulation of electron beams is one step towards truly conformal therapy. This can be realized with the MM50 racetrack microtron that utilizes a scanning beam technique. By adjusting the scan pattern it is possible to obtain arbitrary fluence distributions. Since the monitor chambers in the treatment head are segmented in both x- and y-directions it is possible to verify the fluence distribution to the patient at any time during the treatment. Intensity modulated electron beams have been measured with film and a plane parallel chamber and compared with calculations. The calculations were based on a pencil beam method. An intensity distribution at the multileaf collimator (MLC) level was calculated by superposition of measured pencil beams over scan patterns. By convolving this distribution with a Gaussian pencil beam, which has propagated from the MLC to the isocentre, a fluence distribution at isocentre level was obtained. The agreement between calculations and measurements was within 2% in dose or 1 mm in distance in the penumbra zones. A standard set of intensity modulated electron beams has been developed. These beams have been implemented in a treatment planning system and are used for manual optimization. A clinical example (prostate) of such an application is presented and compared with a standard irradiation technique.
Intensity modulation with electrons: calculations, measurements and clinical applications
Energy Technology Data Exchange (ETDEWEB)
Karlsson, Magnus G.; Karlsson, Mikael [Department of Radiation Physics, Umeaa University, S-901 85 Umeaa (Sweden); Zackrisson, Bjoern [Department of Oncology, Umeaa University, S-901 85 Umeaa (Sweden)
1998-05-01
Intensity modulation of electron beams is one step towards truly conformal therapy. This can be realized with the MM50 racetrack microtron that utilizes a scanning beam technique. By adjusting the scan pattern it is possible to obtain arbitrary fluence distributions. Since the monitor chambers in the treatment head are segmented in both x- and y-directions it is possible to verify the fluence distribution to the patient at any time during the treatment. Intensity modulated electron beams have been measured with film and a plane parallel chamber and compared with calculations. The calculations were based on a pencil beam method. An intensity distribution at the multileaf collimator (MLC) level was calculated by superposition of measured pencil beams over scan patterns. By convolving this distribution with a Gaussian pencil beam, which has propagated from the MLC to the isocentre, a fluence distribution at isocentre level was obtained. The agreement between calculations and measurements was within 2% in dose or 1 mm in distance in the penumbra zones. A standard set of intensity modulated electron beams has been developed. These beams have been implemented in a treatment planning system and are used for manual optimization. A clinical example (prostate) of such an application is presented and compared with a standard irradiation technique. (author)
Halim, Shimaa Abdel; Ibrahim, Magdy A.
2017-02-01
New derivative of heteroannulated chromone identified as 5-methyl-8H-benzo[h]chromeno[2,3-b][1,6]naphthyridine-6(5H),8-dione (5, MBCND) was easily and efficiently synthesized from DBU catalyzed condensation reaction of 2-aminochromone-3-carboxaldehyde (1) with 4-hydroxy-1-methylquinolin-2(1H)-one (2). The same product 5 was isolated from condensation reaction of aldeyde 1 with 3-(4-hydroxy-1-methyl-2-oxo-1,2-dihydroquinolin-3-yl)-3-oxopropanoic acid (3) or ethyl 4-(4-hydroxy-1-methyl-2-oxo-1,2-dihydroquinolin-3-yl)-2,4-dioxobutanoate (4). Structure of compound (5, MBCND) was deduced based on their elemental analyses and spectral data (IR, 1H NMR and mass spectra). Density Functional Theory (DFT) calculations at the B3LYP/6-311G (d,p) level of theory have been carried out to investigate the equilibrium geometry of the novel compound (5, MBCND). Moreover, total energy, energy of HOMO and LUMO and Mullikan atomic charges were calculated. In addition, the dipole moment, theoretical study of the electronic structure, nonlinear optical properties (NLO), and natural bonding orbital (NBO) analysis and orientation have been performed and discussed. Also the electronic absorption spectra were measured in polar (methanol) as well as non polar (dioxane) solvents and the assignment of the observed bands has been discussed by TD-DFT calculations. The correspondences between calculated and experimental transitions energies are satisfactory.
Convergent close-coupling calculations of electron-helium scattering
Energy Technology Data Exchange (ETDEWEB)
Fursa, D.V.; Bray, I. [Flinders Univ. of South Australia, Adelaide, SA (Australia). Electronic Structure of Materials Centre
1996-11-01
We present a review of the recent electron-helium calculations and experiments concentrating on the extensive application of the convergent close-coupling (CCC) method. Elastic, excitation, and ionization processes are considered, as well as excitation of the metastable states. The present status of agreement between theory and experiment for elastic and discrete excitations of the ground state is, in our view, quite satisfactory. However, discrepancies for excitation of the metastable states are substantial and invite urgent attention. Application of the CCC method to the calculation of differential ionization cross sections is encouraging, but also shows some fundamental difficulties. (authors). 92 refs., 15 figs.
Institute of Scientific and Technical Information of China (English)
王岩国; 刘红荣; 杨奇斌; 张泽
2003-01-01
Off-axis electron holography in a field emission gun transmission-electron microscope and electron dynamic calculation are used to determine the absorption coefficient and inelastic mean free path (IMFP) of copper.Dependence of the phase shift of the exit electron wave on the specimen thickness is established by electron dynamic simulation. The established relationship makes it possible to determine the specimen thickness with the calculated phase shift by match of the phase shift measured in the reconstructed phase image. Based on the measured amplitudes in reconstructed exit electron wave and reference wave in the vacuum, the examined IMFP of electron with energy of 200kV in Cu is obtained to be 96nm.
Metallic impurities induced electronic transport in WSe2: First-principle calculations
Li, Hongping; Liu, Shuai; Huang, Songlei; Zhang, Quan; Li, Changsheng; Liu, Xiaojuan; Meng, Jian; Tian, Yi
2016-08-01
Using density functional theory calculations, we have systematically explored the effect of V, Nb and Ta impurities on the electronic transport properties of 2H-WSe2. The formation energies elucidate dopants are preferred to substitute W atoms, and the incorporation of Nb into WSe2 is most thermodynamically favorable. The crystal structures almost hold the pristine WSe2 structure-type in spite of with slightly bond relaxation. More importantly, a pronounced electronic transport behavior has realized in all doped systems, which is mainly triggered by metal impurities. Our calculation suggests chemical doping is an effective way to precisely modulate WSe2 performance for target technological applications.
Electronic, vibrational and related properties of group IV metal oxides by ab initio calculations
Energy Technology Data Exchange (ETDEWEB)
Leite Alves, H.W. [Departamento de Ciencias Naturais, Universidade Federal de Sao Joao del Rei, C.P. 110, Sao Joao del Rei, MG 36301-160 (Brazil)], E-mail: hwlalves@ufsj.edu.br; Silva, C.C. [Departamento de Ciencias Naturais, Universidade Federal de Sao Joao del Rei, C.P. 110, Sao Joao del Rei, MG 36301-160 (Brazil); Lino, A.T. [Departamento de Fisica, Universidade Federal de Uberlandia, C.P. 593, Uberlandia, MG 38400-902 (Brazil); Borges, P.D. [Departamento de Engenharia de Telecomunicacoes, Uniao Educacional de Minas Gerais, Uberlandia, MG 38411-113 (Brazil); Scolfaro, L.M.R. [Instituto de Fisica, Universidade de Sao Paulo, C.P. 66318, Sao Paulo, SP 05315-970 (Brazil); Silva, E.F. da [Departamento de Fisica, Universidade Federal de Pernambuco, Cidade Universitaria, Recife, PE 50670-901 (Brazil)
2008-11-30
We present our theoretical results for the structural, electronic, vibrational and optical properties of MO{sub 2} (M = Sn, Zr, Hf and Ti) obtained by first-principles calculations. Relativistic effects are demonstrated to be important for a realistic description of the detailed structure of the electronic frequency-dependent dielectric function, as well as of the carrier effective masses. Based on our results, we found that the main contribution of the high values calculated for the oxides dielectric constants arises from the vibrational properties of these oxides, and the vibrational static dielectric constant values diminish with increasing pressure.
Calculation of surface dose in rotational total skin electron irradiation
Energy Technology Data Exchange (ETDEWEB)
Pla, C.; Heese, R.; Pla, M.; Podgorsak, E.B.
1984-07-01
A single-field rotational total skin electron irradiation technique has recently been developed at the McGill University for treatment of skin malignancies. The dose received by a given surface point during rotation in a uniform large electron field depends on the radius of rotation of the surface point, on the local radius of curvature of the contour in the vicinity of the point of interest, and on the shadows cast by limbs (arms upon trunk or head and neck, and legs upon each other). A method for calculating the surface dose distribution on a patient is presented accounting for the various parameters affecting the dose. A series of measurements were performed with polystyrene and a humanoid phantom, and an excellent agreement between measured and calculated dose distributions was obtained.
Energy Technology Data Exchange (ETDEWEB)
Lavrentyev, A.A.; Gabrelian, B.V.; Vorzhev, V.B.; Nikiforov, I.Ya. [Department of Physics, Don State Technical University, Gagarin Sq. 1, Rostov-on-Don (Russian Federation); Khyzhun, O.Yu. [Frantsevych Institute for Problems of Materials Science, National Academy of Sciences of Ukraine, 3 Krzhyzhanivsky Str., UA-03142 Kyiv (Ukraine)], E-mail: khyzhun@ipms.kiev.ua; Rehr, J.J. [Department of Physics, University of Washington, Seattle, WA 98195-1560 (United States)
2008-08-25
X-ray photoelectron spectroscopy (XPS), X-ray emission spectroscopy (XES) and X-ray absorption spectroscopy (XAS) methods were employed in the present work to investigate the electronic structure of almost stoichiometric cubic (NaCl structure) Hf{sub x}Ta{sub 1-x}C{sub y} carbides. The XPS valence-band and core-level spectra, the XES bands reflecting energy distributions of mainly the Ta 5d- and C 2p-like states as well as the XAS Ta L{sub III} edges (unoccupied Ta d-like states) were derived and compared on a common energy scale for cubic HfC{sub 0.95}, Hf{sub 0.5}Ta{sub 0.5}C{sub 0.94} and TaC{sub 0.98} compounds. To investigate the influence of substitution of tantalum atoms for hafnium atoms in the Hf{sub x}Ta{sub 1-x}C{sub y} carbides, cluster self-consistent calculations of total and partial densities of states were carried out with the FEFF8 code for HfC, Hf{sub 0.5}Ta{sub 0.5}C and TaC compounds possessing the NaCl-type structure. In the present work a rather good agreement of the experimental and theoretical results for the electronic structure of the Hf{sub x}Ta{sub 1-x}C{sub y} system under study was obtained. The results indicate that a strong hybridization of the Hf(Ta) 5d- and C 2p-like states is characteristic for the Hf{sub x}Ta{sub 1-x}C{sub y} carbides. It has been established that, substitution of hafnium atoms by tantalum atoms in the Hf{sub x}Ta{sub 1-x}C{sub y} system reveals increasing the half-width of the XES C K{alpha} band. When going from HfC{sub 0.95} to TaC{sub 0.98} through the carbide of intermediate composition, the main maximum of the XPS valence-band spectrum shifts in the direction opposite to the position of the Fermi level. In the above sequence of compounds the asymmetry index of the C K{alpha} bands decreases significantly.
First-principles calculations of heat capacities of ultrafast laser-excited electrons in metals
Bévillon, E.; Colombier, J. P.; Recoules, V.; Stoian, R.
2015-05-01
Ultrafast laser excitation can induce fast increases of the electronic subsystem temperature. The subsequent electronic evolutions in terms of band structure and energy distribution can determine the change of several thermodynamic properties, including one essential for energy deposition; the electronic heat capacity. Using density functional calculations performed at finite electronic temperatures, the electronic heat capacities dependent on electronic temperatures are obtained for a series of metals, including free electron like, transition and noble metals. The effect of exchange and correlation functionals and the presence of semicore electrons on electronic heat capacities are first evaluated and found to be negligible in most cases. Then, we tested the validity of the free electron approaches, varying the number of free electrons per atom. This shows that only simple metals can be correctly fitted with these approaches. For transition metals, the presence of localized d electrons produces a strong deviation toward high energies of the electronic heat capacities, implying that more energy is needed to thermally excite them, compared to free sp electrons. This is attributed to collective excitation effects strengthened by a change of the electronic screening at high temperature.
Structure of conduction electrons on polysilanes
Energy Technology Data Exchange (ETDEWEB)
Ichikawa, Tsuneki [Hokkaido Univ., Sapporo (Japan); Kumagai, Jun
1998-10-01
The orbital structures of conduction electrons on permethylated oligosilane, Si{sub 2n}(CH{sub 3}){sub 2n+2}(n = 2 - 8), and poly(cyclohexylmethylsilane) have been determined by the electron spin-echo envelope modulation signals of the radical anions of these silanes in a deuterated rigid matrix at 77 K. The conduction electron on permethylated oligosilane is delocalized over the entire main chain, whereas that on poly(cyclohexylmethylsilane) is localized on a part of the main chain composed of about six Si atoms. Quantum-chemical calculations suggest that Anderson localization due to fluctuation of {sigma} conjugation by conformational disorder of the main chain is responsible for the localization of both the conduction electron and the hole. (author)
Molecular electronic-structure theory
Helgaker, Trygve; Jorgensen, Poul
2013-01-01
Ab initio quantum chemistry is increasingly paired with computational methods to solve intractable problems in chemistry and molecular physics. Now in a paperback edition, this comprehensive and technical work covers all the important aspects of modern molecular electronic-structure theory, clearly explaining quantum-mechanical methods and applications to molecular equilibrium structure, atomization energies, and reaction enthalpies. Extensive numerical examples illustrate each method described. An excellent resource for researchers in quantum chemistry and anyone interested in the theory and its applications.
Electronic structure of hcp transition metals
DEFF Research Database (Denmark)
Jepsen, O.; Andersen, O. Krogh; Mackintosh, A. R.
1975-01-01
Using the linear muffin-tin-orbital method described in the previous paper, we have calculated the electronic structures of the hcp transition metals, Zr, Hf, Ru, and Os. We show how the band structures of these metals may be synthesized from the sp and d bands, and illustrate the effects...... of hybridization, relativistic band shifts, and spin-orbit coupling by the example of Os. By making use of parameters derived from the muffin-tin potential, we discuss trends in the positions and widths of the energy bands, especially the d bands, as a function of the location in the periodic table. The densities...... of states of the four metals are presented, and the calculated heat capacities compared with experiment. The Fermi surfaces of both Ru and Os are found to be in excellent quantitative agreement with de Haas-van Alphen measurements, indicating that the calculated d-band position is misplaced by less than 10...
Institute of Scientific and Technical Information of China (English)
CHEN Ming-Zhi; HE Jian-Hua
2009-01-01
Undulators are key devices to produce brilliant synchrotron radiation at the synchrotron radiation facilities.In this paper we present a numerical computing method,including the computing program that has been developed to calculate the spontaneous radiation emitted from relativistic electrons in undulators by simulating the electrons' trajectory.The effects of electron beam emittance and energy spread have also been taken into account.Comparing with other computing methods available at present,this method has a few advantages with respect to several aspects.It can adopt any measured or arbitrarily simulated 3D magnetic field and arbitrary electron beam pattern for the calculation and it's able to analyze undulators of any type of magnetic structure.It's expected to predict precisely the practical radiation spectrum.The calculation results of a short period in-vacuum undulator and an EllipticaUy Polarized Undulator (EPU) at Shanghai Synchrotron Radiation Facility (SSRF) are presented as examples.
Graph-based linear scaling electronic structure theory
Niklasson, Anders M N; Negre, Christian F A; Cawkwell, Marc J; Swart, Pieter J; Mohd-Yusof, Jamal; Germann, Timothy C; Wall, Michael E; Bock, Nicolas; Djidjev, Hristo
2016-01-01
We show how graph theory can be combined with quantum theory to calculate the electronic structure of large complex systems. The graph formalism is general and applicable to a broad range of electronic structure methods and materials, including challenging systems such as biomolecules. The methodology combines well-controlled accuracy, low computational cost, and natural low-communication parallelism. This combination addresses substantial shortcomings of linear scaling electronic structure theory, in particular with respect to quantum-based molecular dynamics simulations.
Institute of Scientific and Technical Information of China (English)
刘芳; 王茺; 杨瑞东; 李亮; 熊飞; 杨宇
2009-01-01
采用基于密度泛函理论的平面渡超软赝势方法和广义梯度近似,计算了掺杂Ge前后单晶Si中Si-Ge键的布居值、键长以及能带结构和态密度.计算结果表明,Ge掺杂后体系晶格常数发生变化,Ge-Si键变长,布居值及带隙宽度减小.还进一步研究了掺杂Ge后的光学性质,掺杂后静态介电常数值与纯Si相比有所增大,且吸收带宽变窄、吸收带边明显红移,并对这些掺杂诱导的材料物性变化进行了解释.%Using the plane-wave uhrasofe pseudo potential method based on the density functional theory, the electronic structures and optical properties variation in monocrystal silicon before and after Ge doping are studied it. The calculated data are supported by atomic population, band length, band structure and density of states of Si-Ge band in materials. And the results indicate that the band length and atomic population decrease, the crystal lattice constant changes. Furthermore, Ge doping causes the gap to decrease, and meanwhile, it makes static dielectric constant higher and results in red-shift and narrower part of absorption wavelength.
The calculation of satellite line structures in highly stripped plasmas
Energy Technology Data Exchange (ETDEWEB)
Abdallah, J. Jr.; Kilcrease, D.P. [Los Alamos National Lab., NM (United States); Faenov, A.Ya.; Pikuz, T.A. [Multicharged Ion Spectra Data Center, Moscow (Russian Federation)
1998-11-01
This is the final report of a three-year, Laboratory Directed Research and Development (LDRD) project at the Los Alamos National Laboratory (LANL). Recently developed high-resolution x-ray spectrographs have made it possible to measure satellite structures from various plasma sources with great detail. These lines are weak optically thin lines caused by the decay of dielectronic states and generally accompany the resonance lines of H-like and He-like ions. The Los Alamos atomic physics and kinetics codes provide a unique capability for calculating the position and intensities of such lines. These programs have been used to interpret such highly resolved spectral measurements from pulsed power devices and laser produced plasmas. Some of these experiments were performed at the LANL Bright Source and Trident laser facilities. The satellite structures are compared with calculations to diagnose temperatures and densities. The effect of non-thermal electron distributions of electrons on calculated spectra was also considered. Collaborations with Russian scientists have added tremendous value to this research die to their vast experience in x-ray spectroscopy.
Electronic structure investigation of biphenylene films
Totani, R.; Grazioli, C.; Zhang, T.; Bidermane, I.; Lüder, J.; de Simone, M.; Coreno, M.; Brena, B.; Lozzi, L.; Puglia, C.
2017-02-01
Photoelectron Spectroscopy (PS) and Near-Edge X-ray Absorption Fine Structure (NEXAFS) spectroscopy have been used to investigate the occupied and empty density of states of biphenylene films of different thicknesses, deposited onto a Cu(111) crystal. The obtained results have been compared to previous gas phase spectra and single molecule Density Functional Theory (DFT) calculations to get insights into the possible modification of the molecular electronic structure in the film induced by the adsorption on a surface. Furthermore, NEXAFS measurements allowed characterizing the variation of the molecular arrangement with the film thickness and helped to clarify the substrate-molecule interaction.
QWalk: A Quantum Monte Carlo Program for Electronic Structure
Wagner, Lucas K; Mitas, Lubos
2007-01-01
We describe QWalk, a new computational package capable of performing Quantum Monte Carlo electronic structure calculations for molecules and solids with many electrons. We describe the structure of the program and its implementation of Quantum Monte Carlo methods. It is open-source, licensed under the GPL, and available at the web site http://www.qwalk.org
An Emphasis of Electron Energy Calculation in Quantum Wells
Institute of Scientific and Technical Information of China (English)
GAOShao-Wen; CAOJun-Cheng; FENGSong-Lin
2004-01-01
We investigate various methods for the calculation of the electron energy in semiconductor quantum wells and focus on a matrix algorithm method. The results show better fitness of the factor -h2/2 э/эz 1/m*（z） э/эz than that of -h2/2 1/m*（z） э2/эz2 in the first part of the Schroedinger equation. The effect of nonparabolicity in the conduction band is also discussed.
DEFF Research Database (Denmark)
Shim, Irene; Kingcade, Joseph E. , Jr.; Gingerich, Karl A.
1986-01-01
In the present work we present all-electron ab initio Hartree–Fock (HF) and configuration interaction (CI) calculations of six electronic states of the PdGe molecule. The molecule is predicted to have a 3Pi ground state and two low-lying excited states 3Sigma− and 1Sigma+. The electronic structure...
QED Based Calculation of the Fine Structure Constant
Energy Technology Data Exchange (ETDEWEB)
Lestone, John Paul [Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
2016-10-13
Quantum electrodynamics is complex and its associated mathematics can appear overwhelming for those not trained in this field. Here, semi-classical approaches are used to obtain a more intuitive feel for what causes electrostatics, and the anomalous magnetic moment of the electron. These intuitive arguments lead to a possible answer to the question of the nature of charge. Virtual photons, with a reduced wavelength of λ, are assumed to interact with isolated electrons with a cross section of πλ^{2}. This interaction is assumed to generate time-reversed virtual photons that are capable of seeking out and interacting with other electrons. This exchange of virtual photons between particles is assumed to generate and define the strength of electromagnetism. With the inclusion of near-field effects the model presented here gives a fine structure constant of ~1/137 and an anomalous magnetic moment of the electron of ~0.00116. These calculations support the possibility that near-field corrections are the key to understanding the numerical value of the dimensionless fine structure constant.
Electronic Structure and Catalysis on Metal Surfaces
Greeley, Jeff; Norskov, Jens K.; Mavrikakis, Manos
2002-10-01
The powerful computational resources available to scientists today, together with recent improvements in electronic structure calculation algorithms, are providing important new tools for researchers in the fields of surface science and catalysis. In this review, we discuss first principles calculations that are now capable of providing qualitative and, in many cases, quantitative insights into surface chemistry. The calculations can aid in the establishment of chemisorption trends across the transition metals, in the characterization of reaction pathways on individual metals, and in the design of novel catalysts. First principles studies provide an excellent fundamental complement to experimental investigations of the above phenomena and can often allow the elucidation of important mechanistic details that would be difficult, if not impossible, to determine from experiments alone.
DFT calculation of core-electron binding energies
Energy Technology Data Exchange (ETDEWEB)
Takahata, Yuji; Chong, Delano P. E-mail: chong@chem.ubc.ca
2003-11-01
A total of 59 core-electron binding energies (CEBEs) were studied with the Amsterdam Density Functional Program (ADF) program and compared with the observed values. The results indicate that a polarized triple-zeta basis set of Slater-type orbitals is adequate for routine assessment of the performance of each method of computation. With such a basis set, seven density functionals were tested. In addition, the performance of 21 energy density functionals were computed from the density calculated with the statistical average of orbital potentials (SAOP). Among all the choices tested, the best density functional for core-electron binding energies of C to F turns out to be the combination of Perdew-Wang (1986) functional for exchange and the Perdew-Wang (1991) functional for correlation, confirming earlier studies based on contracted Gaussian-type orbitals. For this best functional, five Slater-type orbital basis sets were examined, ranging from polarized double-zeta quality to the largest set available in the ADF package. For the best functional with the best basis set, the average absolute deviation (AAD) of the calculated value from experiment is only 0.16 eV.
Photodissociation of CCH: Classical trajectory calculations involving seven electronic states
Apaydın, Gökşin; Fink, William H.; Jackson, William M.
2004-11-01
The photodissociation dynamics of ethynyl radical, C2H, involving seven electronic states is studied by classical trajectory calculations. Initial values of the trajectories are selected based on relative absorption intensities calculated by Mebel et al. The energies and the derivatives are interpolated by three-dimensional cubic spline interpolator using an extended data pool. Mean square errors and standard deviations in interpolation of energies for 450 data points are found to be in the range 3.1×10-6-1.4×10-5 and 1.7×10-3-3.8×10-3 hartrees, respectively. The photofragments of C2 and H are produced mainly in the X 1Σg+, a 3Πu, b 3Σg-, c 3Σu+, A 1Πu, B 1Δg electronic states of C2 as product. The avoided crossings do not appear to be in the main dissociation pathways. The internal distributions are in good accord with the experimental results where comparison is possible, suggesting that the fragmentation mechanism of C2H2 into C2 and H is a two step process involving C2H radical as an intermediate with a life time long enough to allow complete collection of the phase space in the experiments.
An electronic application for rapidly calculating Charlson comorbidity score
Directory of Open Access Journals (Sweden)
Jani Ashesh B
2004-12-01
Full Text Available Abstract Background Uncertainty regarding comorbid illness, and ability to tolerate aggressive therapy has led to minimal enrollment of elderly cancer patients into clinical trials and often substandard treatment. Increasingly, comorbid illness scales have proven useful in identifying subgroups of elderly patients who are more likely to tolerate and benefit from aggressive therapy. Unfortunately, the use of such scales has yet to be widely integrated into either clinical practice or clinical trials research. Methods This article reviews evidence for the validity of the Charlson Comorbidity Index (CCI in oncology and provides a Microsoft Excel (MS Excel Macro for the rapid and accurate calculation of CCI score. The interaction of comorbidity and malignant disease and the validation of the Charlson Index in oncology are discussed. Results The CCI score is based on one year mortality data from internal medicine patients admitted to an inpatient setting and is the most widely used comorbidity index in oncology. An MS Excel Macro file was constructed for calculating the CCI score using Microsoft Visual Basic. The Macro is provided for download and dissemination. The CCI has been widely used and validated throughout the oncology literature and has demonstrated utility for most major cancers. The MS Excel CCI Macro provides a rapid method for calculating CCI score with or without age adjustments. The calculator removes difficulty in score calculation as a limitation for integration of the CCI into clinical research. The simple nature of the MS Excel CCI Macro and the CCI itself makes it ideal for integration into emerging electronic medical records systems. Conclusions The increasing elderly population and concurrent increase in oncologic disease has made understanding the interaction between age and comorbid illness on life expectancy increasingly important. The MS Excel CCI Macro provides a means of increasing the use of the CCI scale in clinical
DEFF Research Database (Denmark)
Christensen, N. Egede; Feuerbacher, B.
1974-01-01
The electronic energy-band structure of tungsten has been calculated by means of the relativistic-augmented-plane-wave method. A series of mutually related potentials are constructed by varying the electronic configuration and the amount of Slater exchange included. The best band structure...
Calculation of Electronic Absorption Spectra with Account of Thermal Geometry Fluctuations
Guzha, Maris V.; Svitenkov, Andrew I.
2016-08-01
An influence of thermal fluctuations of molecule's geometry on calculated electronic-absorption Vis/Uv spectra is considered. Paper presents the quantum chemical modeling of the electronic-absorption spectra for the collection of graphene samples (44, 56, 60, 68 atoms). The calculations were performed by time dependent density functional theory (TDDFT) method in combination with molecular dynamics (MD) simulation at T=300 K. The noticeable changing of spectra relative to single point TDDFT calculation was discovered for two of four structures. We associate achieved results with perturbation of hydrogen and carbon atoms on the edges of the structures. We believe that suggested methodology will be useful in application engineering researches of novel molecules and molecular complexes.
Structural Dynamics of Electronic Systems
Suhir, E.
2013-03-01
The published work on analytical ("mathematical") and computer-aided, primarily finite-element-analysis (FEA) based, predictive modeling of the dynamic response of electronic systems to shocks and vibrations is reviewed. While understanding the physics of and the ability to predict the response of an electronic structure to dynamic loading has been always of significant importance in military, avionic, aeronautic, automotive and maritime electronics, during the last decade this problem has become especially important also in commercial, and, particularly, in portable electronics in connection with accelerated testing of various surface mount technology (SMT) systems on the board level. The emphasis of the review is on the nonlinear shock-excited vibrations of flexible printed circuit boards (PCBs) experiencing shock loading applied to their support contours during drop tests. At the end of the review we provide, as a suitable and useful illustration, the exact solution to a highly nonlinear problem of the dynamic response of a "flexible-and-heavy" PCB to an impact load applied to its support contour during drop testing.
Correlated electronic structure of CeN
Energy Technology Data Exchange (ETDEWEB)
Panda, S.K., E-mail: swarup.panda@physics.uu.se [Department of Physics and Astronomy, Uppsala University, P.O. Box 516, SE-751 20 Uppsala (Sweden); Di Marco, I. [Department of Physics and Astronomy, Uppsala University, P.O. Box 516, SE-751 20 Uppsala (Sweden); Delin, A. [Department of Physics and Astronomy, Uppsala University, P.O. Box 516, SE-751 20 Uppsala (Sweden); KTH Royal Institute of Technology, School of Information and Communication Technology, Department of Materials and Nano Physics, Electrum 229, SE-164 40 Kista (Sweden); KTH Royal Institute of Technology, Swedish e-Science Research Center (SeRC), SE-100 44 Stockholm (Sweden); Eriksson, O., E-mail: olle.eriksson@physics.uu.se [Department of Physics and Astronomy, Uppsala University, P.O. Box 516, SE-751 20 Uppsala (Sweden)
2016-04-15
Highlights: • The electronic structure of CeN is studied within the GGA+DMFT approach using SPTF and Hubbard I approximation. • 4f spectral functions from SPTF and Hubbard I are coupled to explain the various spectroscopic manifestations of CeN. • The calculated XPS and BIS spectra show good agreement with the corresponding experimental spectra. • The contribution of the various l-states and the importance of cross-sections for the photoemission process are analyzed. - Abstract: We have studied in detail the electronic structure of CeN including spin orbit coupling (SOC) and electron–electron interaction, within the dynamical mean-field theory combined with density-functional theory in generalized gradient approximation (GGA+DMFT). The effective impurity problem has been solved through the spin-polarized T-matrix fluctuation-exchange (SPTF) solver and the Hubbard I approximation (HIA). The calculated l-projected atomic partial densities of states and the converged potential were used to obtain the X-ray-photoemission-spectra (XPS) and Bremstrahlung Isochromat spectra (BIS). Following the spirit of Gunnarsson–Schonhammer model, we have coupled the SPTF and HIA 4f spectral functions to explain the various spectroscopic manifestations of CeN. Our computed spectra in such a coupled scheme explain the experimental data remarkably well, establishing the validity of our theoretical model in analyzing the electronic structure of CeN. The contribution of the various l-states in the total spectra and the importance of cross sections are also analyzed in detail.
The electronic structure of impurities in semiconductors
Nylandsted larsen, A; Svane, A
2002-01-01
The electronic structure of isolated substitutional or interstitial impurities in group IV, IV-IV, and III-V compound semiconductors will be studied. Mössbauer spectroscopy will be used to investigate the incorporation of the implanted isotopes on the proper lattice sites. The data can be directly compared to theoretical calculations using the LMTO scheme. Deep level transient spectroscopy will be used to identify the band gap levels introduced by metallic impurities, mainly in Si~and~Si$ _{x}$Ge$_{1-x}$. \\\\ \\\\
Lattice Boltzmann Model for Electronic Structure Simulations
Mendoza, M; Succi, S
2015-01-01
Recently, a new connection between density functional theory and kinetic theory has been proposed. In particular, it was shown that the Kohn-Sham (KS) equations can be reformulated as a macroscopic limit of the steady-state solution of a suitable single-particle kinetic equation. By using a discrete version of this new formalism, the exchange and correlation energies of simple atoms and the geometrical configuration of the methane molecule were calculated accurately. Here, we discuss the main ideas behind the lattice kinetic approach to electronic structure computations, offer some considerations for prospective extensions, and also show additional numerical results, namely the geometrical configuration of the water molecule.
Molecular electronic-structure theory
Helgaker, Trygve; Olsen, Jeppe
2014-01-01
Ab initio quantum chemistry has emerged as an important tool in chemical research and is appliced to a wide variety of problems in chemistry and molecular physics. Recent developments of computational methods have enabled previously intractable chemical problems to be solved using rigorous quantum-mechanical methods. This is the first comprehensive, up-to-date and technical work to cover all the important aspects of modern molecular electronic-structure theory. Topics covered in the book include: * Second quantization with spin adaptation * Gaussian basis sets and molecular-integral evaluati
Calculation of Electron Beam Potential Energy from RF Photocathode Gun
Liu Wan Ming; Power, John G; Wang, Haitao
2005-01-01
In this paper, we consider the contribution of potential energy to beam dynamics as simulated by PARMELA at low energies (10 - 30MeV). We have developed a routine to calculate the potential energy of the relativistic electron beam using the static coulomb potential in the rest frame (first order approximation as in PARMELA). We found that the potential energy contribution to the beam dynamics could be very significant, particularly with high charge beams generated by an RF photocathode gun. Our results show that when the potential energy is counted correctly and added to the kinetic energy from PARMELA, the total energy is conserved. Simulation results of potential and kinetic energies for short beams (~1 mm) at various charges (1 - 100 nC) generated by a high current RF photocathode gun are presented.
Dramatic changes in electronic structure revealed by fractionally charged nuclei
Energy Technology Data Exchange (ETDEWEB)
Cohen, Aron J. [Department of Chemistry, Lensfield Rd., University of Cambridge, Cambridge CB2 1EW (United Kingdom); Mori-Sánchez, Paula, E-mail: paula.mori@uam.es [Departamento de Química, Universidad Autónoma de Madrid, 28049 Madrid (Spain)
2014-01-28
Discontinuous changes in the electronic structure upon infinitesimal changes to the Hamiltonian are demonstrated. These are revealed in one and two electron molecular systems by full configuration interaction (FCI) calculations when the realm of the nuclear charge is extended to be fractional. FCI electron densities in these systems show dramatic changes in real space and illustrate the transfer, hopping, and removal of electrons. This is due to the particle nature of electrons seen in stretched systems and is a manifestation of an energy derivative discontinuity at constant number of electrons. Dramatic errors of density functional theory densities are seen in real space as this physics is missing from currently used approximations. The movements of electrons in these simple systems encapsulate those in real physical processes, from chemical reactions to electron transport and pose a great challenge for the development of new electronic structure methods.
Dramatic changes in electronic structure revealed by fractionally charged nuclei
Cohen, Aron J.; Mori-Sánchez, Paula
2014-01-01
Discontinuous changes in the electronic structure upon infinitesimal changes to the Hamiltonian are demonstrated. These are revealed in one and two electron molecular systems by full configuration interaction (FCI) calculations when the realm of the nuclear charge is extended to be fractional. FCI electron densities in these systems show dramatic changes in real space and illustrate the transfer, hopping, and removal of electrons. This is due to the particle nature of electrons seen in stretched systems and is a manifestation of an energy derivative discontinuity at constant number of electrons. Dramatic errors of density functional theory densities are seen in real space as this physics is missing from currently used approximations. The movements of electrons in these simple systems encapsulate those in real physical processes, from chemical reactions to electron transport and pose a great challenge for the development of new electronic structure methods.
Electronic structure and equilibrium properties of hcp titanium and zirconium
Indian Academy of Sciences (India)
B P Panda
2012-08-01
The electronic structures of hexagonal-close-packed divalent titanium (3-d) and zirconium (4-d) transition metals are studied by using a non-local model potential method. From the present calculation of energy bands, Fermi energy, density of states and the electronic heat capacity of these two metals are determined and compared with the existing results in the literature.
Analysis of boron carbides' electronic structure
Howard, Iris A.; Beckel, Charles L.
1986-01-01
The electronic properties of boron-rich icosahedral clusters were studied as a means of understanding the electronic structure of the icosahedral borides such as boron carbide. A lower bound was estimated on bipolaron formation energies in B12 and B11C icosahedra, and the associated distortions. While the magnitude of the distortion associated with bipolaron formation is similar in both cases, the calculated formation energies differ greatly, formation being much more favorable on B11C icosahedra. The stable positions of a divalent atom relative to an icosahedral borane was also investigated, with the result that a stable energy minimum was found when the atom is at the center of the borane, internal to the B12 cage. If incorporation of dopant atoms into B12 cages in icosahedral boride solids is feasible, novel materials might result. In addition, the normal modes of a B12H12 cluster, of the C2B10 cage in para-carborane, and of a B12 icosahedron of reduced (D sub 3d) symmetry, such as is found in the icosahedral borides, were calculated. The nature of these vibrational modes will be important in determining, for instance, the character of the electron-lattice coupling in the borides, and in analyzing the lattice contribution to the thermal conductivity.
Energy Technology Data Exchange (ETDEWEB)
Franca, Fernando
1995-12-31
In this work we investigate the local magnetic properties and the electronic structure of HCP Fe, as well introducing transition metals atoms 3d (Cs, Ti, Cr, Mn, Co, Ni, Cu, Zn) in HCP iron matrix. We employed the discrete variational method (DVM), which is an orbital molecular method which incorporate the Hartree-Fock-Slater theory and the linear combination of atomic orbitals (LCAO), in the self-consistent charge approximation and the local density approximation of Von Barth and Hedin to the exchange-correlation potential. We used the embedded cluster model to investigate the electronic structure and the local magnetic properties for the central atom of a cluster of 27 atoms immersed in the microcrystal representing the HCP Fe. (author) 32 refs., 19 figs., 2 tabs.
Electronic properties of tantalum pentoxide polymorphs from first-principles calculations
Energy Technology Data Exchange (ETDEWEB)
Lee, J. [Department of Materials Science and Engineering, University of Michigan, Ann Arbor 48109 (United States); Department of Electrical Engineering and Computer Science, University of Michigan, Ann Arbor 48109 (United States); Lu, W. [Department of Electrical Engineering and Computer Science, University of Michigan, Ann Arbor 48109 (United States); Kioupakis, E., E-mail: kioup@umich.edu [Department of Materials Science and Engineering, University of Michigan, Ann Arbor 48109 (United States)
2014-11-17
Tantalum pentoxide (Ta{sub 2}O{sub 5}) is extensively studied for its attractive properties in dielectric films, anti-reflection coatings, and resistive switching memory. Although various crystalline structures of tantalum pentoxide have been reported, its structural, electronic, and optical properties still remain a subject of research. We investigate the electronic and optical properties of crystalline and amorphous Ta{sub 2}O{sub 5} structures using first-principles calculations based on density functional theory and the GW method. The calculated band gaps of the crystalline structures are too small to explain the experimental measurements, but the amorphous structure exhibits a strong exciton binding energy and an optical band gap (∼4 eV) in agreement with experiment. We determine the atomic orbitals that constitute the conduction band for each polymorph and analyze the dependence of the band gap on the atomic geometry. Our results establish the connection between the underlying structure and the electronic and optical properties of Ta{sub 2}O{sub 5}.
Electronic structure and magnetism of ThFeAsN
Wang, Guangtao; Shi, Xianbiao
2016-03-01
The electronic structure and magnetic properties of ThFeAsN, a newly discovered superconductor, are investigated by means of first-principles calculations. ThFeAsN shares electronic structure and magnetic properties similar to those of LaOFeAs. Its calculated ground state is the stripe antiferromagnetic state. The hole-like Fermi surfaces (FSs) along the Γ\\text-Z line largely overlap with the electron-like FS along the M\\text-A line with the vector q= (π, π, 0) . Such significant FS nesting induces a peak of the bare susceptibility χ0(q ) at the M-point.
Bannikov, V. V.; Shein, I. R.; Ivanovskii, A. L.
2012-01-01
Using the first principles FLAPW-GGA method, comparative study of structural, electronic properties and of chemical bonding in four 1111-like chalcogenide oxides La MChO (LaCuSO, LaCuSeO, LaAgSO, and LaAgSeO) with ZrCuSiAs-type structure was performed. Our studies showed that: (i) replacements of d metal atoms (Cu ↔ Ag) and chalcogen atoms (S ↔ Se) lead to anisotropic deformations of the crystal structure; this effect is related to strong anisotropy of inter-atomic bonds; (ii) all of the examined chalcogenide oxides are semiconducting; the band gap decreases both at S → Se and Cu → Ag substitutions; and (iii) the bonding in La MChO phases can be classified as a high-anisotropic mixture of ionic and covalent contributions, where mixed covalent-ionic bonds take place inside [La 2O 2] and [ M2Ch2] blocks, whereas between the adjacent [La 2O 2]/[ M2Ch2] blocks, ionic bonds emerge owing to [La 2O 2] → [ M2Ch2] charge transfer. Since the near-Fermi bands of La MChO phases originate mainly from electronic states of [ M2Ch2] blocks, we speculate that chemical substitutions inside these blocks can result in striking differences in electronic properties of these systems; therefore, this approach can be promising for significant enlargement of the functional properties of these materials.
Mancera, L; Takeuchi, N
2003-01-01
We have studied the structural and electronic properties of YN in rock salt (sodium chloride), caesium chloride, zinc blende and wurtzite structures using first-principles total energy calculations. Rock salt is the calculated ground state structure with a = 4.93 A, B sub 0 = 157 GPa. The experimental lattice constant is a = 4.877 A. There is an additional local minimum in the wurtzite structure with total energy 0.28 eV/unit cell higher. At high pressure (approx 138 GPa), our calculations predict a phase transformation from a NaCl to a CsCl structure.
Synthesis, characterization and DFT calculations of electronic and optical properties of YbPO4
Khadraoui, Z.; Horchani-Naifer, K.; Ferhi, M.; Ferid, M.
2015-08-01
YbPO4 crystals were synthesized by solid-state reaction and characterized by X-ray diffraction, infrared and Raman spectroscopies. The electronic structure and optical properties of YbPO4 such as the energy band structures, density of states and chemical bonds were calculated with the Density Functional Theory (DFT) for the first time. We present a combination of the GGA and the LDA + U approaches in order to obtain appropriate results due to the strong Coulomb repulsion between the highly localized 4f electrons of rare earth atoms. The linear photon-energy-dependent dielectric functions, conductivity and some optical constants such as refractive index, reflectivity and absorption coefficients were determined. The calculated total and partial densities of states indicate that the top of valance band is built upon O-2p states with P-3p states via σ (P-O) interactions, and the conduction bands mostly originate from Yb-5d states.
Halogen versus halide electronic structure
Institute of Scientific and Technical Information of China (English)
Willem-Jan; van; Zeist; F.Matthias; Bickelhaupt
2010-01-01
Halide anions X-are known to show a decreasing proton affinity(PA),as X descends in the periodic table along series F,Cl,Br and I.But it is also well-known that,along this series,the halogen atom X becomes less electronegative(or more electropositive).This corresponds to an increasing energy of the valence np atomic orbital(AO) which,somewhat contradictorily,suggests that the electron donor capability and thus the PA of the halides should increase along the series F,Cl,Br,I.To reconcile these contradictory observations,we have carried out a detailed theoretical analysis of the electronic structure and bonding capability of the halide anions X-as well as the halogen radicals X-,using the molecular orbital(MO) models contained in Kohn-Sham density functional theory(DFT,at SAOP/TZ2P as well as OLYP/TZ2P levels) and ab initio theory(at the HF/TZ2P level).We also resolve an apparent intrinsic contradiction in Hartree-Fock theory between orbital-energy and PA trends.The results of our analyses are of direct relevance for understanding elementary organic reactions such as nucleophilic substitution(SN2) and base-induced elimination(E2) reactions.
Calculating electron momentum densities and Compton profiles using the linear tetrahedron method.
Ernsting, D; Billington, D; Haynes, T D; Millichamp, T E; Taylor, J W; Duffy, J A; Giblin, S R; Dewhurst, J K; Dugdale, S B
2014-12-10
A method for computing electron momentum densities and Compton profiles from ab initio calculations is presented. Reciprocal space is divided into optimally-shaped tetrahedra for interpolation, and the linear tetrahedron method is used to obtain the momentum density and its projections such as Compton profiles. Results are presented and evaluated against experimental data for Be, Cu, Ni, Fe3Pt, and YBa2Cu4O8, demonstrating the accuracy of our method in a wide variety of crystal structures.
Electronically excited states of chloroethylenes: Experiment and DFT calculations in comparison
Energy Technology Data Exchange (ETDEWEB)
Khvostenko, O.G., E-mail: khv@mail.ru
2014-08-15
Highlights: • B3LYP/6-311 + G(d,p) calculations of chloroethylenes molecules were performed. • Calculations were correlated with experiment on the molecules ground and excited states. • The general pattern of electron structure of chloroethylenes was obtained. • Necessity of this data for chloroethylenes negative ions study was noted. - Abstract: B3LYP/6-311 + G(d,p) calculations of ground and electronically excited states of ethylene, chloroethylene, 1,1-dichloroethylene, 1,2-dichloroethylene-cis, 1,2-dichloroethylene-trans trichloroethylene and tetrachloroethylene molecules have been performed. Molecular orbitals images and orbital correlation diagram are given. The calculation results for chloroethylenes electronically excited states were compared with experimental data from the energy-loss spectra obtained and generally considered previously by C.F. Koerting, K.N. Walzl and A. Kupperman. Several new additional triplet and singlet transitions were pointed out in these spectra considering the calculation results. The finding of the additional transitions was supported by the UV absorption spectrum of trichloroethylene recorded in big cuvette (10 cm), where the first three triplet and two low-intensive forbidden singlet transitions were registered. The first triplet of this compound was recorded to be at the same energy as was found with the energy-loss spectroscopy.
Bannikov, V. V.; Ivanovskii, A. L.
2013-06-01
By means of the FLAPW-GGA approach, we have systematically studied the structural and electronic properties of tetragonal dichalcogenides KNi2Ch2 (Ch=S, Se, and Te). Our results show that replacements of chalcogens (S→Se→Te) lead to anisotropic deformations of the crystals structure, which are related to the strong anisotropic character of the inter-atomic bonds, where inside the [Ni2Ch2] blocks, mixed covalent-ionic-metallic bonds occur, whereas between the adjacent [Ni2Ch2] blocks and K atomic sheets, ionic bonds emerge. We found that in the sequence KNi2S2→KNi2Se2→KNi2Te2 (i) the overall band structure (where the near-Fermi valence bands are due mainly to the Ni states) is preserved, but the width of the common valence band and the widths of the separate sub-bands and the gaps decrease; (ii) the total DOSs at the Fermi level also decrease; and (iii) for the Fermi surfaces, the most appreciable changes are demonstrated by the hole-like sheets, when a necklace-like topology is formed for the 2D-like sheets and the volume of the closed pockets decreases. Some trends in structural and electronic parameters for ThCr2Si2-type layered dichalcogenides, KNi2Ch2, KFe2Ch2, KCo2Se2, are discussed.
Electronic structure investigation of novel superconductors
Energy Technology Data Exchange (ETDEWEB)
Buling, Anna
2014-05-15
The discovery of superconductivity in iron-based pnictides in 2008 gave rise to a high advance in the research of high-temperature superconductors. But up to now there is no generally admitted theory of the non-BCS mechanism of these superconductors. The electron and hole doped Ba122 (BaFe{sub 2}As{sub 2}) compounds investigated in this thesis are supposed to be suitable model systems for studying the electronic behavior in order to shed light on the superconducting mechanisms. The 3d-transition metal doped Ba122 compounds are investigated using the X-ray photoelectron spectroscopy (XPS), X-ray absorption spectroscopy (XAS), X-ray emission spectroscopy (XES) and X-ray magnetic circular dichroism (XMCD), while the completely hole doped K122 is observed using XPS. The experimental measurements are complemented by theoretical calculations. A further new class of superconductors is represented by the electride 12CaO*7Al{sub 2}O{sub 3}: Here superconductivity can be realized by electrons accommodated in the crystallographic sub-nanometer-sized cavities, while the mother compound is a wide band gap insulator. Electronic structure investigations, represented by XPS, XAS and resonant X-ray photoelectron spectroscopy (ResPES), carried out in this work, should help to illuminate this unconventional superconductivity and resolve a debate of competing models for explaining the existence of superconductivity in this compound.
Electronic and optical properties of AlN under pressure: DFT calculations
Javaheri, Sahar; Boochani, Arash; Babaeipour, Manuchehr; Naderi, Sirvan
2017-01-01
Structural, elastic, optical, and electronic properties of wurtzite (WZ), zinc-blende (ZB), and rocksalt (RS) structures of AlN are investigated using the first-principles method and within the framework of density functional theory (DFT). Lattice parameters, bulk modulus, shear modulus, Young’s modulus, and elastic constants are calculated at zero pressure and compared with other experimental and theoretical results. The wurtzite and zinc-blende structures have a transition to rocksalt phase at the pressures of 12.7 GPa and 14 GPa, respectively. The electronic properties are calculated using both GGA and EV-GGA approximations; the obtained results by EV-GGA approximation are in much better agreement with the available experimental data. The RS phase has the largest bandgap with an amount of 4.98 eV; by increasing pressure, this amount is also increased. The optical properties like dielectric function, energy loss function, refractive index, and extinction coefficient are calculated under pressure using GGA approximation. Inter-band transitions are investigated using the peaks of imaginary part of the dielectric function and these transitions mainly occur from N-2p to Al-3p levels. The results show that the RS structure has more different properties than the WZ and ZB structures.
DEFF Research Database (Denmark)
Strange, M.; Rostgaard, Carsten; Hakkinen, H.
2011-01-01
The electronic conductance of a benzene molecule connected to gold electrodes via thiol, thiolate, or amino anchoring groups is calculated using nonequilibrium Green functions in combination with the fully self-consistent GW approximation for exchange and correlation. The calculated conductance...... suggest that more complex gold-thiolate structures where the thiolate anchors are chemically passivated by Au adatoms are responsible for the measured conductance. Analysis of the energy level alignment obtained with DFT, Hartree-Fock, and GW reveals the importance of self-interaction corrections...
Dai, Peng; Jiang, Nan; Tan, Ren-Xiang
2016-01-01
Elucidation of absolute configuration of chiral molecules including structurally complex natural products remains a challenging problem in organic chemistry. A reliable method for assigning the absolute stereostructure is to combine the experimental circular dichroism (CD) techniques such as electronic and vibrational CD (ECD and VCD), with quantum mechanics (QM) ECD and VCD calculations. The traditional QM methods as well as their continuing developments make them more applicable with accuracy. Taking some chiral natural products with diverse conformations as examples, this review describes the basic concepts and new developments of QM approaches for ECD and VCD calculations in solution and solid states.
Gao, Haiyuan; Li, Meijiao; Guo, Zhendong; Chen, Hongshen; Jin, Zhonghe; Yu, Bin
2011-01-01
Electronic transport properties of monolayer graphene with extreme physical bending up to 90o angle are studied using ab Initio first-principle calculations. The importance of key structural parameters including step height, curvature radius and bending angle are discussed how they modify the transport properties of the deformed graphene sheet comparing to the corresponding flat ones. The local density of state reveals that energy state modification caused by the physical bending is highly localized. It is observed that the transport properties of bent graphene with a wide range of geometrical configurations are insensitive to the structural deformation in the low-energy transmission spectra, even in the extreme case of bending. The results support that graphene, with its superb electromechanical robustness, could serve as a viable material platform in a spectrum of applications such as photovoltaics, flexible electronics, OLED, and 3D electronic chips.
Considerations of beta and electron transport in internal dose calculations
Energy Technology Data Exchange (ETDEWEB)
Bolch, W.E.; Poston, J.W. Sr.
1990-12-01
Ionizing radiation has broad uses in modern science and medicine. These uses often require the calculation of energy deposition in the irradiated media and, usually, the medium of interest is the human body. Energy deposition from radioactive sources within the human body and the effects of such deposition are considered in the field of internal dosimetry. In July of 1988, a three-year research project was initiated by the Nuclear Engineering Department at Texas A M University under the sponsorship of the US Department of Energy. The main thrust of the research was to consider, for the first time, the detailed spatial transport of electron and beta particles in the estimation of average organ doses under the Medical Internal Radiation Dose (MIRD) schema. At the present time (December of 1990), research activities are continuing within five areas. Several are new initiatives begun within the second or third year of the current contract period. They include: (1) development of small-scale dosimetry; (2) development of a differential volume phantom; (3) development of a dosimetric bone model; (4) assessment of the new ICRP lung model; and (5) studies into the mechanisms of DNA damage. A progress report is given for each of these tasks within the Comprehensive Report. In each case, preliminary results are very encouraging and plans for further research are detailed within this document.
First-principles calculations of electronic and magnetic properties of CeN: The LDA + U method
Hao, Ai-Min; Bai, Jing
2013-10-01
Electronic and magnetic properties of CeN are investigated using first-principles calculations based on density functional theory (DFT) with the LDA + U method. Our results show that CeN is a half-metal. The majority-spin electron band structure has metallic intersections, whereas the minority-spin electron band structure has a semiconducting gap straddling the Fermi level. A small indirect energy gap occurs between X and W. The calculated magnetic moment is 0.99 μB per unit cell.
Spek, Anthony L
2015-01-01
The completion of a crystal structure determination is often hampered by the presence of embedded solvent molecules or ions that are seriously disordered. Their contribution to the calculated structure factors in the least-squares refinement of a crystal structure has to be included in some way. Traditionally, an atomistic solvent disorder model is attempted. Such an approach is generally to be preferred, but it does not always lead to a satisfactory result and may even be impossible in cases where channels in the structure are filled with continuous electron density. This paper documents the SQUEEZE method as an alternative means of addressing the solvent disorder issue. It conveniently interfaces with the 2014 version of the least-squares refinement program SHELXL [Sheldrick (2015). Acta Cryst. C71. In the press] and other refinement programs that accept externally provided fixed contributions to the calculated structure factors. The PLATON SQUEEZE tool calculates the solvent contribution to the structure factors by back-Fourier transformation of the electron density found in the solvent-accessible region of a phase-optimized difference electron-density map. The actual least-squares structure refinement is delegated to, for example, SHELXL. The current versions of PLATON SQUEEZE and SHELXL now address several of the unnecessary complications with the earlier implementation of the SQUEEZE procedure that were a necessity because least-squares refinement with the now superseded SHELXL97 program did not allow for the input of fixed externally provided contributions to the structure-factor calculation. It is no longer necessary to subtract the solvent contribution temporarily from the observed intensities to be able to use SHELXL for the least-squares refinement, since that program now accepts the solvent contribution from an external file (.fab file) if the ABIN instruction is used. In addition, many twinned structures containing disordered solvents are now also
Ab initio calculation of the electronic absorption spectrum of liquid water
Energy Technology Data Exchange (ETDEWEB)
Martiniano, Hugo F. M. C.; Galamba, Nuno [Grupo de Física Matemática da Universidade de Lisboa, Av. Professor Gama Pinto 2, 1649-003 Lisboa (Portugal); Cabral, Benedito J. Costa, E-mail: ben@cii.fc.ul.pt [Grupo de Física Matemática da Universidade de Lisboa, Av. Professor Gama Pinto 2, 1649-003 Lisboa (Portugal); Departamento de Química e Bioquímica, Faculdade de Ciências, Universidade de Lisboa, 1749-016 Lisboa (Portugal); Instituto de Física da Universidade de São Paulo, CP 66318, 05314-970 São Paulo, SP (Brazil)
2014-04-28
The electronic absorption spectrum of liquid water was investigated by coupling a one-body energy decomposition scheme to configurations generated by classical and Born-Oppenheimer Molecular Dynamics (BOMD). A Frenkel exciton Hamiltonian formalism was adopted and the excitation energies in the liquid phase were calculated with the equation of motion coupled cluster with single and double excitations method. Molecular dynamics configurations were generated by different approaches. Classical MD were carried out with the TIP4P-Ew and AMOEBA force fields. The BLYP and BLYP-D3 exchange-correlation functionals were used in BOMD. Theoretical and experimental results for the electronic absorption spectrum of liquid water are in good agreement. Emphasis is placed on the relationship between the structure of liquid water predicted by the different models and the electronic absorption spectrum. The theoretical gas to liquid phase blue-shift of the peak positions of the electronic absorption spectrum is in good agreement with experiment. The overall shift is determined by a competition between the O–H stretching of the water monomer in liquid water that leads to a red-shift and polarization effects that induce a blue-shift. The results illustrate the importance of coupling many-body energy decomposition schemes to molecular dynamics configurations to carry out ab initio calculations of the electronic properties in liquid phase.
Electronic structure of heterocyclic ring chain polymers
Brocks, Geert; Tol, Arie
1999-01-01
The band gaps, ionization potentials and electron affinities of conjugated chain polymers comprising heterocyclic aromatic rings are studied systematically as a function of atomic substitutions with N, O and S using first principles density functional calculations.
Reversible Hydrogen Storage Materials – Structure, Chemistry, and Electronic Structure
Energy Technology Data Exchange (ETDEWEB)
Robertson, Ian M. [University of Wisconsin-Madison; Johnson, Duane D. [Ames Lab., Iowa
2014-06-21
To understand the processes involved in the uptake and release of hydrogen from candidate light-weight metal hydride storage systems, a combination of materials characterization techniques and first principle calculation methods have been employed. In addition to conventional microstructural characterization in the transmission electron microscope, which provides projected information about the through thickness microstructure, electron tomography methods were employed to determine the three-dimensional spatial distribution of catalyst species for select systems both before and after dehydrogenation. Catalyst species identification as well as compositional analysis of the storage material before and after hydrogen charging and discharging was performed using a combination of energy dispersive spectroscopy, EDS, and electron energy loss spectroscopy, EELS. The characterization effort was coupled with first-principles, electronic-structure and thermodynamic techniques to predict and assess meta-stable and stable phases, reaction pathways, and thermodynamic and kinetic barriers. Systems studied included:NaAlH4, CaH2/CaB6 and Ca(BH4)2, MgH2/MgB2, Ni-Catalyzed Magnesium Hydride, TiH2-Catalyzed Magnesium Hydride, LiBH4, Aluminum-based systems and Aluminum
Kim, Sejoong; Lee, Hyun-Woo
2006-05-01
A pioneering experiment [E. Schuster, E. Buks, M. Heiblum, D. Mahalu, V. Umansky, and Hadas Shtrikman, Nature 385, 417 (1997)] reported the measurement of the transmission phase of an electron traversing a quantum dot and found the intriguing feature of a sudden phase drop in the conductance valleys. Based on the Friedel sum rule for a spinless effective one-dimensional system, it has been previously argued [H.-W. Lee, Phys. Rev. Lett. 82, 2358 (1999)] that the sudden phase drop should be accompanied by the vanishing of the transmission amplitude, or transmission zero. Here we address roles of strong electron-electron interactions on the electron transport through a two-level quantum dot where one level couples with the leads much more strongly than the other level does [P. G. Silvestrov and Y. Imry, Phys. Rev. Lett. 85, 2565 (2000)]. We perform a perturbative conductance calculation with an explicit account of large charging energy and verify that the resulting conductance exhibits transmission zero, in agreement with the analysis based on the Friedel sum rule.
Method for calculating ionic and electronic defect concentrations in y-stabilised zirconia
Energy Technology Data Exchange (ETDEWEB)
Poulsen, F.W. [Risoe National Lab., Materials Research Dept., Roskilde (Denmark)
1997-10-01
A numerical (trial and error) method for calculation of concentration of ions, vacancies and ionic and electronic defects in solids (Brouwer-type diagrams) is presented. No approximations or truncations of the set of equations describing the chemistry for the various defect regions are used. Doped zirconia and doped thoria with simultaneous presence of protonic and electronic defects are taken as examples: 7 concentrations as function of oxygen partial pressure and/or water vapour partial pressure are determined. Realistic values for the equilibrium constants for equilibration with oxygen gas and water vapour, as well as for the internal equilibrium between holes and electrons were taken from the literature. The present mathematical method is versatile - it has also been employed by the author to treat more complex systems, such as perovskite structure oxides with over- and under-stoichiometry in oxygen, cation vacancies and simultaneous presence of protons. (au) 6 refs.
First-Principles Correlated Electron Calculations of Photoabsorption in Small Sodium Clusters
Priya, Pradip Kumar; Shukla, Alok
2016-01-01
We present correlated electron calculations of the linear photoabsorption spectra of small neutral closed- and open-shell sodium clusters (Na$_{n}$, n=2-6), as well as closed-shell cation clusters (Na$_{n}$$^{+}$, n=3, 5). We have employed the configuration interaction (CI) methodology at the full CI (FCI) and quadruple CI (QCI) levels to compute the ground, and the low-lying excited states of the clusters. For most clusters, besides the minimum energy structures, we also consider their energetically close isomers. The photoabsorption spectra were computed under the electric-dipole approximation, employing the dipole-matrix elements connecting the ground state with the excited states of each isomer. Our calculations were tested rigorously for convergence with respect to the basis set, as well as with respect to the size of the active orbital space employed in the CI calculations. Excellent quantitative agreement is observed between our results, and experiments, where available.
Electronic structures and physical properties of pure aluminum metal
Institute of Scientific and Technical Information of China (English)
谢佑卿; 刘心笔
1999-01-01
By one-atom theory, the electronic structure of pure Al metal with f.c.c, structure has been determined to be [Ne]（3sc）1.8790（3pc）0.4982（3sf+3pf）0.6228. According to this electronic structure, the potential curve, lattice constant, cohesive energy, elastisity, and the temperature dependence of the linear thermal expansion coefficients have been calculated. The electronic structures and characteristic properties of Al metals with b. c. c., h.c.p. structures and liquid have been studied. It is argued that the pure Al metal with f. c.c. structure can exist naturally, but with b. c. c.and h. c.p. structures cannot.##属性不符
Energy Technology Data Exchange (ETDEWEB)
Deleuze, M.S.; Pickup, B.T.; Wilton, D.J.
2000-04-05
The authors present the theory of the electron propagator perturbed by an external electric field and show how it can be used to calculate a variety of one-electron linear response properties that are accurate through second order in electron correlation. Some illustrative calculations are discussed.
Studies on electronic structure of GaN(0001) surface
Xie Chang Kun; Xu Fa Qiang; Deng Rui; Liu Feng; Yibulaxin, K
2002-01-01
An electronic structure investigation on GaN(0001) is reported. The authors employ a full-potential linearized augmented plane-wave (FPLAPW) approach to calculate the partial density of state, which is in agreement with previous experimental results. The effects of the Ga3d semi-core levels on the electronic structure of GaN are discussed. The valence-electronic structure of the wurtzite GaN(0001) surface is investigated using synchrotron radiation excited angle-resolved photoemission spectroscopy. The bulk bands dispersion along GAMMA A direction in the Brillouin zones is measured using normal-emission spectra by changing photon-energy. The band structure derived from authors' experimental data is compared well with the results of authors' FPLAPW calculation. Furthermore, off-normal emission spectra are also measured along the GAMMA K and GAMMA M directions. Two surface states are identified, and their dispersions are characterized
Yang, Hua
2012-01-01
Electronic structure and optical properties of α-FeMO 3 systems (M = Sc, Ti, V, Cr, Cu, Cd or In) have been investigated using first principles calculations. All of the FeMO 3 systems have a large net magnetic moment. The ground state of pure α-Fe 2O 3 is an antiferromagnetic insulator. For M = Cu or Cd, the systems are half-metallic. Strong absorption in the visible region can be observed in the Cu and Cd-doped systems. Systems with M = Sc, Ti, V, Cr or In are not half-metallic and are insulators. The strongest peaks shift toward shorter wavelengths in the absorption spectra. It is concluded that transition metal doping can modify the electronic structure and optical properties of α-FeMO 3 systems. This journal is © 2012 The Royal Society of Chemistry.
First-principles calculations on electronic structures of B-doped SrTiO3%B掺杂SrTiO 3电子结构的第一性原理计算
Institute of Scientific and Technical Information of China (English)
刘晨吉; 贾云龙; 刘红; 吴一; 刘磊; 郑树凯
2016-01-01
利用基于密度泛函理论(DFT)的第一性原理平面波超软赝势法，对未掺杂、B替位Sr、B替位Ti、B替位O和B间隙掺杂SrTiO 3的晶格参数、Mulliken电荷布居、能带结构、态密度和光吸收系数进行计算。结果表明：B替位Sr和B替位Ti掺杂对SrTiO3电子结构和光学性质的影响不显著；B替位O掺杂则在SrTiO3的禁带中引入3条杂质能级，杂质能级上的电子可以吸收能量较小的光子跃迁至导带，光吸收强度从可见光长波段550 nm开始逐渐增加，光谱吸收边红移；B以间隙原子的形式掺杂时，SrTiO 3的禁带宽度大幅增大，电子跃迁能增加，光谱吸收边蓝移。%The lattice parameters, Mulliken charge populations, energy band structures, density of states and absorption coefficients of pure SrTiO3, B substitutes for Sr or Ti, and interstitial B doped SrTiO3 were studied by the first-principles plane wave ultra-soft pseudo-potential method based on the density functional theory (DFT). The results show that the impacts on the electronic structures and optical properties of SrTiO3 are not significant when the B atom substitutes for the Sr or Ti atom. When B substitutes for O atom, three impurity levels are introduced into the band gap of SrTiO3, the electrons on the impurity levels can transit to the conduction band by absorbing photon of less energy, the intensity of light absorption begins to increase gradually from visible light wavelength of 550 nm and the spectral absorption edge has a red shift. When B is in the form of interstitial, the width of forbidden band of SrTiO3 enlarges significantly and the transition energy of the electrons increases, which results in the blue shift of the spectral absorption edge.
Institute of Scientific and Technical Information of China (English)
ZHOU Chun-Mei; WU Zhen-Dong; HUANG Xiao-Long
2005-01-01
Calculations of energies and absolute intensities of Auger electron and X-ray arising from electron capture are introduced briefly. The calculation codes and main process are also presented. The application is also given by taking 55Fe ε decay as an example.
Energy Technology Data Exchange (ETDEWEB)
Akdim, Brahim, E-mail: brahim.akdim.ctr@us.af.mil, E-mail: ruth.pachter@us.af.mil [Air Force Research Laboratory, Materials and Manufacturing Directorate, Wright-Patterson Air Force Base, Ohio 45433 (United States); General Dynamics Information Technology, Inc., 500 Springfield Pike, Dayton, Ohio 454331 (United States); Pachter, Ruth, E-mail: brahim.akdim.ctr@us.af.mil, E-mail: ruth.pachter@us.af.mil; Naik, Rajesh R. [Air Force Research Laboratory, Materials and Manufacturing Directorate, Wright-Patterson Air Force Base, Ohio 45433 (United States)
2015-05-04
In this letter, we report on the evaluation of diphenylalanine (FF), dityrosine (YY), and phenylalanine-tryptophan (FW) self-assembled peptide nanotube structures for electronics and photonics applications. Realistic bulk peptide nanotube material models were used in density functional theory calculations to mimic the well-ordered tubular nanostructures. Importantly, validated functionals were applied, specifically by using a London dispersion correction to model intertube interactions and a range-separated hybrid functional for accurate bandgap calculations. Bandgaps were found consistent with available experimental data for FF, and also corroborate the higher conductance reported for FW in comparison to FF peptide nanotubes. Interestingly, the predicted bandgap for the YY tubular nanostructure was found to be slightly higher than that of FW, suggesting higher conductance as well. In addition, the band structure calculations along the high symmetry line of nanotube axis revealed a direct bandgap for FF. The results enhance our understanding of the electronic properties of these material systems and will pave the way into their application in devices.
Magnetic Field and Force Calculations for ATLAS Asymmetrical Structure
Nessi, Marzio
2001-01-01
Magnetic field distortion in the assymetrical ATLAS structure are calculated. Magnetic forces in the system are estimated. 3D magnetic field simulation by the Opera3D code for symmetrical and asymmetrical systems is used.
Structure of thallium and lead calculated from Shaw local pseudopotential and molecular dynamics
Directory of Open Access Journals (Sweden)
Gasser J. G.
2011-05-01
Full Text Available Recently, we (Es Sbihi Phil. Mag 2010 have successfully calculated, by molecular dynamics, the static structure factor of liquid bismuth at different temperatures. Our results were in very good agreement with the Waseda experimental data. Our assumption was to consider the true density of states which presents a gap as measured by Indlekofer (J. Non-Cryst. Solids 1989 and calculated by Hafner-Jank (Phys. Rev. B 1990 for liquid bismuth. The number of electrons at the Fermi energy has been calculated with three conduction electrons for bismuth (number of p electrons. With this assumption, the structures were determined with an effective ion-ion potential constructed from the Shaw local Optimised Model Potential (OMP and the Ichimaru-Utsumi dielectric function. In the present paper, we generalize our assumptions to liquid thallium and lead which also present such a gap. Their calculated structures are also very close to the experimental ones. This confirms that the number of conduction electrons on the Fermi sphere is consistent with the number of p electrons as has been even shown for our electronic transport properties of liquid lead (A. Ben Abdellah, Phys. Rev. B 2003.
Application and electronic structure of high-permittivity dielectrics
Energy Technology Data Exchange (ETDEWEB)
Perevalov, Timofei V; Gritsenko, Vladimir A [Rzhanov Institute of Semiconductor Physics, Siberian Branch of the Russian Academy of Sciences, Novosibirsk (Russian Federation)
2010-09-07
Major applications of high-permittivity dielectric materials in silicon devices are reviewed. The basics and software implementations of the electron density functional method are considered. Results of first-principle calculations of the electronic structure are analyzed for the three most important and promising high-permittivity dielectrics, Al{sub 2}O{sub 3}, HfO{sub 2}, and TiO{sub 2}. (reviews of topical problems)
Strain-induced changes to the electronic structure of germanium
Tahini, H. A.
2012-04-17
Density functional theory calculations (DFT) are used to investigate the strain-induced changes to the electronic structure of biaxially strained (parallel to the (001), (110) and (111) planes) and uniaxially strained (along the [001], [110] and [111] directions) germanium (Ge). It is calculated that a moderate uniaxial strain parallel to the [111] direction can efficiently transform Ge to a direct bandgap material with a bandgap energy useful for technological applications. © 2012 IOP Publishing Ltd.
Molecular and Electronic Structure of n-Alkyl Cyanobiphenyl Nematogens
Energy Technology Data Exchange (ETDEWEB)
Risser, Steven M.(TEXAS A and M UNIVERSITY); Ferris, Kim F.(BATTELLE (PACIFIC NW LAB))
2001-12-01
First principle electronic structure calculations (ab-initio and density functional) were performed on a series of substituted cyanobiphenyls to examine the structural and electronic properties as a function of the alkyl tail length and changes in torsion angle about the central bond connecting the rings. We find good agreement between our results and previous electronic structure studies for the optimized torsion angle between phenyls in the cyanobiphenyls, and changes in dipole moment for the cyanobiphenyls. We also find the torsion angle and rotational barriers in cyanobiphenyls to be similar to that in simple biphenyl. However, we find large discrepancies with the recent density functional calculations that reported a much smaller torsion angle in the syanobiphenyls.
Electron tomography of dislocation structures
Energy Technology Data Exchange (ETDEWEB)
Liu, G.S.; House, S.D.; Kacher, J. [Department of Materials Science and Engineering, University of Illinois at Urbana-Champaign, 1304 W. Green St., Urbana, IL 61801 (United States); Tanaka, M.; Higashida, K. [Department of Materials Science and Engineering, Kyushu University, 744 Motooka, Nishi-ku, Fukuoka 819-0395 (Japan); Robertson, I.M., E-mail: irobertson@wisc.edu [Department of Materials Science and Engineering, University of Illinois at Urbana-Champaign, 1304 W. Green St., Urbana, IL 61801 (United States); Department of Materials Science and Engineering, University of Wisconsin-Madison, Madison, WI 53706 (United States)
2014-01-15
Recent developments in the application of electron tomography for characterizing microstructures in crystalline solids are described. The underlying principles for electron tomography are presented in the context of typical challenges in adapting the technique to crystalline systems and in using diffraction contrast imaging conditions. Methods for overcoming the limitations associated with the angular range, the number of acquired images, and uniformity of image contrast are introduced. In addition, a method for incorporating the real space coordinate system into the tomogram is presented. As the approach emphasizes development of experimental solutions to the challenges, the solutions developed and implemented are presented in the form of examples.
Atomic and electronic structure of exfoliated black phosphorus
Energy Technology Data Exchange (ETDEWEB)
Wu, Ryan J.; Topsakal, Mehmet; Jeong, Jong Seok; Wentzcovitch, Renata M.; Mkhoyan, K. Andre, E-mail: mkhoyan@umn.edu [Department of Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, Minnesota 55455 (United States); Low, Tony; Robbins, Matthew C.; Haratipour, Nazila; Koester, Steven J. [Department of Electrical and Computer Engineering, University of Minnesota, Minneapolis, Minnesota 55455 (United States)
2015-11-15
Black phosphorus, a layered two-dimensional crystal with tunable electronic properties and high hole mobility, is quickly emerging as a promising candidate for future electronic and photonic devices. Although theoretical studies using ab initio calculations have tried to predict its atomic and electronic structure, uncertainty in its fundamental properties due to a lack of clear experimental evidence continues to stymie our full understanding and application of this novel material. In this work, aberration-corrected scanning transmission electron microscopy and ab initio calculations are used to study the crystal structure of few-layer black phosphorus. Directly interpretable annular dark-field images provide a three-dimensional atomic-resolution view of this layered material in which its stacking order and all three lattice parameters can be unambiguously identified. In addition, electron energy-loss spectroscopy (EELS) is used to measure the conduction band density of states of black phosphorus, which agrees well with the results of density functional theory calculations performed for the experimentally determined crystal. Furthermore, experimental EELS measurements of interband transitions and surface plasmon excitations are also consistent with simulated results. Finally, the effects of oxidation on both the atomic and electronic structure of black phosphorus are analyzed to explain observed device degradation. The transformation of black phosphorus into amorphous PO{sub 3} or H{sub 3}PO{sub 3} during oxidation may ultimately be responsible for the degradation of devices exposed to atmosphere over time.
Electronic-Structure-Based Design of Ordered Alloys
DEFF Research Database (Denmark)
Bligaard, Thomas; Andersson, M.P.; Jacobsen, Karsten Wedel
2006-01-01
We describe some recent advances in the methodology of using electronic structure calculations for materials design. The methods have been developed for the design of ordered metallic alloys and metal alloy catalysts, but the considerations we present are relevant for the atomic-scale computation...
Electronic structure of Fe- vs. Ru-based dye molecules
DEFF Research Database (Denmark)
Johnson, Phillip S.; Cook, Peter L.; Zegkinoglou, Ioannis;
2013-01-01
In order to explore whether Ru can be replaced by inexpensive Fe in dye molecules for solar cells, the differences in the electronic structure of Fe- and Ru-based dyes are investigated by X-ray absorption spectroscopy and first-principles calculations. Molecules with the metal in a sixfold...
CLOPW: a mixed basis set full potential electronic structure method
Bekker, Hermie Gerhard
1997-01-01
This thesis is about the development of the full potental CLOPW package for electronic structure calculations. Chapter 1 provides the necessary background in the theory of solid state physics. It gives a short overview of the effective one particle model as commonly used in solid state physics. It a
LDA +U calculation of electronic and thermoelectric properties of doped CuCoO 2
Knížek, K.
2015-02-01
Doped CuCoO2 is a candidate oxide material for thermoelectric power generation. The evolution of the band structure and thermoelectric properties of CuCoO2 upon hole and electron doping in the CoO2 layer and hole doping at the Cu site were calculated by the local-density approximation (LDA) and LDA +U methods and using standard Boltzmann theory. The doping was simulated by the virtual atom approximation and the supercell approach and the results were compared with previous calculations using the rigid band approximation. The calculated thermopowers are comparable for the virtual atom and rigid band approximations, but the thermopower obtained from the supercell calculation is significantly lower. The reason is the similar energy of Co and Cu d orbitals and the hybridization of symmetrically related Co a1 g and Cu dz2 orbitals. As a consequence, both cations contribute to the bands around the Fermi level and hence a substitution at any of the cation sites alters the band structure at EF and affects the thermoelectric properties. Our results show that in the case of hole doping, higher thermopower is obtained for substitution at the Cu site than in the CoO2 layer.
The equivalent potential of water molecules for electronic structure of lysine
Institute of Scientific and Technical Information of China (English)
LI ChunJie; ZHENG HaoPing; WANG XueMei
2007-01-01
In order to get more reliable electronic structures of proteins in aqueous solution,it is necessary to construct a potential of water molecules for protein's electronic structure calculation.The lysine is a hydrophilic amino acid.It is positively charged (Lys+) in neutral water solution.The first-principles,all-electron,ab initio calculations,based on the density functional theory,have been performed to construct such an equivalent potential of water molecules for lysine (Lys+).The process consists of three parts.First,the electronic structure of the cluster containing Lys+ and water molecules is calculated.By adjusting the positions of water molecules,the geometric structure of the cluster having minimum total energy is determined.Then,based on the structure,the electronic structure of Lys+ with the potential of water molecules is calculated using the self-consistent cluster-embedding (SCCE) method.Finally,the electronic structure of Lys+ with the potential of dipoles is calculated.The dipoles are adjusted so that the electronic structure of Lys+ with the potential of dipoles is close to that of water molecules.Thus the equivalent potential of water molecules for the electronic structure of lysine is obtained.The major effect of water molecules on lysine's electronic structure is raising the occupied eigenvalues about 0.5032 eV,and broadening energy gap 89%.The effect of water molecules on the electronic structure of lysine can be simulated by dipoles potential.
The equivalent potential of water molecules for electronic structure of lysine
Institute of Scientific and Technical Information of China (English)
2007-01-01
In order to get more reliable electronic structures of proteins in aqueous solution, it is necessary to construct a potential of water molecules for protein’s electronic structure calculation. The lysine is a hydrophilic amino acid. It is positively charged (Lys+) in neutral water solution. The first-principles, all-electron, ab initio calcula-tions, based on the density functional theory, have been performed to construct such an equivalent potential of water molecules for lysine (Lys+). The process consists of three parts. First, the electronic structure of the cluster containing Lys+ and water molecules is calculated. By adjusting the positions of water molecules, the geometric structure of the cluster having minimum total energy is determined. Then, based on the structure, the electronic structure of Lys+ with the potential of water molecules is calculated using the self-consistent cluster-embedding (SCCE) method. Finally, the electronic structure of Lys+ with the potential of dipoles is calculated. The dipoles are adjusted so that the electronic structure of Lys+ with the potential of dipoles is close to that of water molecules. Thus the equivalent potential of water molecules for the electronic structure of lysine is obtained. The major effect of water molecules on lysine’s electronic structure is raising the occupied eigenvalues about 0.5032 eV, and broadening energy gap 89%. The effect of water molecules on the electronic structure of lysine can be simulated by dipoles potential.
Complex structures of dense lithium: Electronic origin
Degtyareva, V. F.
2016-11-01
Lithium—the lightest alkali metal exhibits unexpected structures and electronic behavior at high pressures. Like the heavier alkali metals, Li is bcc at ambient pressure and transforms first to fcc (at 7.5 GPa). The post-fcc high-pressure form Li-cI 16 (at 40-60 GPa) is similar to Na-cI 16 and related to more complex structures of heavy alkalis Rb-oC52 and Cs- oC84. The other high pressure phases for Li (oC88, oC40, oC24) observed at pressures up to 130 GPa are found only in Li. The different route of Li high-pressure structures correlates with its special electronic configuration containing the only 3 electrons (at 1s and 2s levels). Crystal structures for Li are analyzed within the model of Fermi sphere-Brillouin zone interactions. Stability of post-fcc structures for Li are supported by the Hume-Rothery arguments when new diffraction plains appear close to the Fermi level producing pseudogaps near the Fermi level and decreasing the crystal energy. The filling of Brillouin-Jones zones by electron states for a given structure defines the physical properties as optical reflectivity, electrical resistivity and superconductivity. To understand the complexity of structural and physical properties of Li above 60 GPa it is necessary to assume the valence electron band overlap with the core electrons and increase the valence electron count under compression.
Electronic structure and ionicity of actinide oxides from first principles
DEFF Research Database (Denmark)
Petit, Leon; Svane, Axel; Szotek, Z.
2010-01-01
The ground-state electronic structures of the actinide oxides AO, A2O3, and AO2 (A=U, Np, Pu, Am, Cm, Bk, and Cf) are determined from first-principles calculations, using the self-interaction corrected local spin-density approximation. Emphasis is put on the degree of f-electron localization, whi...... lanthanide oxides. The ionic nature of the actinide oxides emerges from the fact that only those compounds will form where the calculated ground-state valency agrees with the nominal valency expected from a simple charge counting....
Efficient method for calculating electronic bound states in arbitrary one-dimensional quantum wells
de Aquino, V. M.; Iwamoto, H.; Dias, I. F. L.; Laureto, E.; da Silva, M. A. T.; da Silva, E. C. F.; Quivy, A. A.
2017-01-01
In the present paper it is demonstrated that the bound electronic states of multiple quantum wells structures may be calculated very efficiently by expanding their eigenstates in terms of the eigenfunctions of a particle in a box. The bound states of single and multiple symmetric or nonsymmetric wells are calculated within the single-band effective mass approximation. A comparison is then made between the results obtained for simple cases with exact calculations. We also apply our approach to a GaAs/AlGaAs multiple quantum well structure composed of forty periods each one with seven quantum wells. The method may be very useful to design narrow band quantum cascade photodetectors to work without applied bias in a photovoltaic mode. With the presented method the effects of a electric field may also be easily included which is very important if one desires study quantum well structures for application to the development of quantum cascade lasers. The advantages of the method are also presented.
Banded electron structures in the plasmasphere
Energy Technology Data Exchange (ETDEWEB)
Burke, W.J.; Rubin, A.G.; Hardy, D.A.; Holeman, E.G.
1995-05-01
The low-energy plasma analyzer on CRRES has detected significant fluxes of 10-eV to 30-keV electrons trapped on plasmaspheric field lines. On energy versus time spectrograms these electrons appear as banded structures that can span the 2 < L < 6 range of magnetic shells. The authors present an example of banded electron structures, encountered in the nightside plasmasphere during the magnetically quiet January 30, 1991. Empirical analysis suggests that two clouds of low energy electrons were injected from the plasma sheet to L < 4 on January 26 and 27 while the convective electric field was elevated. The energies of electrons in the first cloud were greater than those in the second. DMSP F8 measurements show that after the second injection, the polar cap potential rapidly decreased from >50 to <20 kY. Subsequent encounters with the lower energy cloud on alternating CRRES orbits over the next 2 days showed a progressive, earthward movement of the electrons, inner boundary. Whistler and electron cyclotron harmonic emissions accompanied the most intense manifestations of cloud electrons. The simplest explanation of these measurements is that after initial injection, the AIfven boundary moved Outward, leaving the cloud electrons on closed drift paths. Subsequent fluctuations of the convective electric field penetrated the plasmasphere, transporting cloud elements inward. The magnetic shell distribution of electron temperatures in one of the banded structures suggests that radiative energy losses may be comparable in magnitude to gains due to adiabatic compression.
DEFF Research Database (Denmark)
Eriksson, Olle; Johansson, Börje; Brooks, M. S. S.
1989-01-01
The electronic structure and magnetic properties of some yttrium and uranium Laves-phase pseudobinary alloys with 3d elements have been calculated. The calculations were done by simulating the electronic structure of the alloy by that of an ordered compound with the same stoichiometry. In general...
MODY - calculation of ordered structures by symmetry-adapted functions
Białas, Franciszek; Pytlik, Lucjan; Sikora, Wiesława
2016-01-01
In this paper we focus on the new version of computer program MODY for calculations of symmetryadapted functions based on the theory of groups and representations. The choice of such a functional frame of coordinates for description of ordered structures leads to a minimal number of parameters which must be used for presentation of such structures and investigations of their properties. The aim of this work is to find those parameters, which are coefficients of a linear combination of calculated functions, leading to construction of different types of structure ordering with a given symmetry. A spreadsheet script for simplification of this work has been created and attached to the program.
Energy Technology Data Exchange (ETDEWEB)
Yao, Y. X. [Ames Lab., Ames, IA (United States); Liu, Jun [Ames Lab., Ames, IA (United States); Wang, Cai-Zhuang [Ames Lab., Ames, IA (United States); Ho, Kai-Ming [Ames Lab., Ames, IA (United States)
2014-01-23
We generalized the commonly used Gutzwiller approximation for calculating the electronic structure and total energy of strongly correlated electron systems. In our method, the evaluation of one-body and two-body density matrix elements of the Hamiltonian is simplified using a renormalization approximation to achieve better scaling of the computational effort as a function of system size. To achieve a clear presentation of the concept and methodology, we describe the detailed formalism for a finite hydrogen system with minimal basis set. We applied the correlation matrix renormalization approximation approach to a H_{2} dimer and H_{8} cubic fragment with minimal basis sets, as well as a H_{2} molecule with a large basis set. The results compare favorably with sophisticated quantum chemical calculations. We believe our approach can serve as an alternative way to build up the exchange-correlation energy functional for an improved density functional theory description of systems with strong electron correlations.
Suess, Christian J; Hirst, Jonathan D; Besley, Nicholas A
2017-04-01
The development of optical multidimensional spectroscopic techniques has opened up new possibilities for the study of biological processes. Recently, ultrafast two-dimensional ultraviolet spectroscopy experiments have determined the rates of tryptophan → heme electron transfer and excitation energy transfer for the two tryptophan residues in myoglobin (Consani et al., Science, 2013, 339, 1586). Here, we show that accurate prediction of these rates can be achieved using Marcus theory in conjunction with time-dependent density functional theory. Key intermediate residues between the donor and acceptor are identified, and in particular the residues Val68 and Ile75 play a critical role in calculations of the electron coupling matrix elements. Our calculations demonstrate how small changes in structure can have a large effect on the rates, and show that the different rates of electron transfer are dictated by the distance between the heme and tryptophan residues, while for excitation energy transfer the orientation of the tryptophan residues relative to the heme is important. © 2017 The Authors Journal of Computational Chemistry Published by Wiley Periodicals, Inc.
Synthesis, Crystal Structural Investigations, and DFT Calculations of Novel Thiosemicarbazones
Directory of Open Access Journals (Sweden)
Brian J. Anderson
2016-02-01
Full Text Available The crystal and molecular structures of three new thiosemicarbazones, 2-[1-(2-hydroxy-5-methoxyphenylethylidene]-N-methyl-hydrazinecarbothioamide monohydrate (1, 2-[1-(2-hydroxy-5-methoxyphenylethylidene]-N-ethyl-hydrazinecarbothioamide (2 and 2-[1-(2-hydroxy-4-methoxyphenylethylidene]-N-ethyl-hydrazinecarbothioamide acetonitrile solvate (3, are reported and confirmed by single crystal X-ray diffraction, NMR and UV-vis spectroscopic data. Compound (1, C11H15N3O2S·H2O, crystallizes in the monoclinic with space group P21/c, with cell parameters a = 8.2304(3 Å, b = 16.2787(6 Å, c = 9.9708(4 Å, and β = 103.355(4°. Compound (2, C12H17N3O2S, crystallizes in the C2/c space group with cell parameters a = 23.3083(6 Å, b = 8.2956(2 Å, c = 13.5312(3 Å, β = 91.077(2°. Compound (3, C11H15N3O2S·C2H3N, crystallizes in the triclinic P-1 space group with cell constants a = 8.9384(7 Å, b = 9.5167(8 Å, c = 10.0574(8 Å, α = 110.773(7°, β = 92.413(6°, and γ = 90.654(7°. DFT B3LYP/6-31(G geometry optimized molecular orbital calculations were also performed and frontier molecular orbitals of each compound are displayed. The correlations between the calculated molecular orbital energies (eV for the surfaces of the frontier molecular orbitals to the electronic excitation transitions from the absorption spectra of each compound have been proposed. Additionally, similar correlations observed among three closely related compounds, (4, 2-[1-(2-hydroxy-4-methoxyphenylethylidene]-N-methyl-hydrazinecarbothioamide, (5, 2-[1-(2-hydroxy-6-methoxyphenylethylidene]-N-methyl-hydrazinecarbothioamide acetonitrile monosolvate and (6, 2-[1-(2-hydroxy-6-methoxyphenylethylidene]-N-ethyl-hydrazinecarbothioamide, examining structural differences from the substitution of the methoxy group from the phenyl ring (4, 5, or 6 position and the substitution of the terminal amine (methyl or ethyl to their frontier molecular orbital surfaces and from their Density Functional
Epitaxial graphene electronic structure and transport
Energy Technology Data Exchange (ETDEWEB)
De Heer, Walt A; Berger, Claire; Wu Xiaosong; Sprinkle, Mike; Hu Yike; Ruan Ming; First, Phillip N [School of Physics, Georgia Institute of Technology, Atlanta, GA 30332 (United States); Stroscio, Joseph A [Center for Nanoscale Science and Technology, NIST, Gaithersburg, MD 20899 (United States); Haddon, Robert [Center for Nanoscale Science and Engineering, Departments of Chemistry and Chemical and Environmental Engineering, University of California, Riverside, CA 92521 (United States); Piot, Benjamin; Faugeras, Clement; Potemski, Marek [LNCMI -CNRS, Grenoble, 38042 Cedex 9 (France); Moon, Jeong-Sun, E-mail: walt.deheer@physics.gateh.ed [HRL Laboratories LLC, Malibu, CA 90265 (United States)
2010-09-22
Since its inception in 2001, the science and technology of epitaxial graphene on hexagonal silicon carbide has matured into a major international effort and is poised to become the first carbon electronics platform. A historical perspective is presented and the unique electronic properties of single and multilayered epitaxial graphenes on electronics grade silicon carbide are reviewed. Early results on transport and the field effect in Si-face grown graphene monolayers provided proof-of-principle demonstrations. Besides monolayer epitaxial graphene, attention is given to C-face grown multilayer graphene, which consists of electronically decoupled graphene sheets. Production, structure and electronic structure are reviewed. The electronic properties, interrogated using a wide variety of surface, electrical and optical probes, are discussed. An overview is given of recent developments of several device prototypes including resistance standards based on epitaxial graphene quantum Hall devices and new ultrahigh frequency analogue epitaxial graphene amplifiers.
Electronic structure of Fe-based superconductors
Indian Academy of Sciences (India)
Kalobaran Maiti
2015-06-01
Fe-based superconductors have drawn much attention during the last decade due to the presence of superconductivity in materials containing the magnetic element, Fe, and the coexistence of superconductivity and magnetism. Extensive study of the electronic structure of these systems suggested the dominant role of states in their electronic properties, which is significantly different from the cuprate superconductors. In this article, some of our studies of the electronic structure of these fascinating systems employing high-resolution photoemission spectroscopy is reviewed. The combined effect of electron correlation and covalency reveals an interesting scenario in their electronic structure. The contribution of ligand states at the Fermi level is found to be much more significant than indicated in earlier studies. Temperature evolution of the energy bands reveals the signature of transition akin to Lifshitz transition in these systems.
Electronic structures of MnB soft magnet
Directory of Open Access Journals (Sweden)
Jihoon Park
2016-05-01
Full Text Available We have calculated the electronic structure of MnB using first-principles calculations based on the density functional theory within the local-spin-density approximation. The temperature dependence of saturation magnetization [Ms(T] was calculated by mean field approximation. The calculated density of states (DOS shows that the energy region near the Fermi energy (EF is mostly attributed to the d bands of Mn. The saturation magnetizations (Ms of MnB were calculated to be 964.5 emu/cm3 (1.21 T at 0 K and 859.3 emu/cm3 (1.08 T at 300 K. The calculated Ms at 300 K is in good agreement with experimental Ms of 851.5 emu/cm3.
Parquet decomposition calculations of the electronic self-energy
Gunnarsson, O.; Schäfer, T.; LeBlanc, J. P. F.; Merino, J.; Sangiovanni, G.; Rohringer, G.; Toschi, A.
2016-06-01
The parquet decomposition of the self-energy into classes of diagrams, those associated with specific scattering processes, can be exploited for different scopes. In this work, the parquet decomposition is used to unravel the underlying physics of nonperturbative numerical calculations. We show the specific example of dynamical mean field theory and its cluster extensions [dynamical cluster approximation (DCA)] applied to the Hubbard model at half-filling and with hole doping: These techniques allow for a simultaneous determination of two-particle vertex functions and self-energies and, hence, for an essentially "exact" parquet decomposition at the single-site or at the cluster level. Our calculations show that the self-energies in the underdoped regime are dominated by spin-scattering processes, consistent with the conclusions obtained by means of the fluctuation diagnostics approach [O. Gunnarsson et al., Phys. Rev. Lett. 114, 236402 (2015), 10.1103/PhysRevLett.114.236402]. However, differently from the latter approach, the parquet procedure displays important changes with increasing interaction: Even for relatively moderate couplings, well before the Mott transition, singularities appear in different terms, with the notable exception of the predominant spin channel. We explain precisely how these singularities, which partly limit the utility of the parquet decomposition and, more generally, of parquet-based algorithms, are never found in the fluctuation diagnostics procedure. Finally, by a more refined analysis, we link the occurrence of the parquet singularities in our calculations to a progressive suppression of charge fluctuations and the formation of a resonance valence bond state, which are typical hallmarks of a pseudogap state in DCA.
Directory of Open Access Journals (Sweden)
Isabella Natali Sora
2012-01-01
Full Text Available Quantum mechanics density functional calculations provided gas-phase electron distributions and proton affinities for several mono- and diaza[5]helicenes; computational results, together with experimental data concerning crystal structures and propensity to methylation of the nitrogen atom(s, provide a basis for designing azahelicene complexes with transition metal ions.
R-matrix calculation of low-energy electron collisions with LiH
Energy Technology Data Exchange (ETDEWEB)
Antony, B K [Centre of Molecular and Optical Sciences, Open University, Milton Keynes (United Kingdom); Joshipura, K N [Department of Physics, Sardar Patel University, Vallabh Vidyanagar, 388 120 Gujarat (India); Mason, N J [Centre of Molecular and Optical Sciences, Open University, Milton Keynes (United Kingdom); Tennyson, Jonathan [Department of Physics and Astronomy, University College London, Gower St., London WC1E 6BT (United Kingdom)
2004-04-28
Calculations are performed for electron scattering from LiH. These show that use of a close-coupled expansion gives results significantly different from calculations performed at the static exchange level employed in all previous calculations. In particular the close-coupled calculations find a Feshbach resonance which follows the first excited, a{sup 3}{sigma}{sup -}, state curve. This resonance could provide a route to dissociative attachment and electron impact vibrational excitation. Elastic scattering cross sections, which are very large, as well as inelastic cross sections for excitation to the four lowest electronically excited states are presented as a function of LiH bond length.
Electronic structure of NiO: Correlation and band effects
Energy Technology Data Exchange (ETDEWEB)
Shen, Z. (Stanford Electronics Laboratory, Stanford University, Stanford, California (USA)); List, R.S. (Los Alamos National Laboratory, Los Alamos, New Mexico (USA)); Dessau, D.S.; Wells, B.O. (Stanford Electronics Laboratory, Stanford University, Stanford, California (USA)); Jepsen, O. (Max-Planck-Institute for Solid State Research, D-7000 Stuttgart 80 (Federal Republic of Germany)); Arko, A.J.; Barttlet, R. (Los Alamos National Laboratory, Los Alamos, New Mexico (USA)); Shih, C.K. (Department of Physics, University of Texas, Austin, Texas (USA)); Parmigiani, F. (IBM Research Division, Almaden Research Center, 650 Harry Road, San Jose, California (USA)); Huang, J.C.; Lindberg, P.A.P. (Stanford Electronics Laboratory, Stanford University, Stanford, California (USA))
1991-08-15
We have performed angle-resolved-photoemission experiments and local-density-functional (LDA) band calculations on NiO to study correlation and band effects of this conceptually important compound. Our experimental result suggests a dual nature of the electronic structure of NiO. On the one hand, the LDA band calculation has some relevance to the electronic structure of NiO, and the inclusion of the antiferromagnetic order is essential. For the lower O 2{ital p} bands, the LDA calculation agrees almost perfectly with experimental energy positions and dispersion relations. On the other hand, discrepancies between the experiment and the LDA calculation do exist, especially for the Ni 3{ital d} bands and the O 2{ital p} bands that are heavily mixed with the Ni 3{ital d} bands. It appears that the main discrepancies between the experimental results and the LDA calculation are concentrated in the regions of the insulating gap and the valence-band satellite. In addition to these results, we also report the interesting angle and photon-energy dependence of the satellite emission. The above results show that the angle-resolved-photoemission studies can provide much additional information about the electronic structure of correlated materials like NiO.
One-Electron Theory of Metals. Cohesive and Structural Properties
DEFF Research Database (Denmark)
Skriver, Hans Lomholt
The work described in the report r.nd the 16 accompanying publications is based upon a one-electron theory obtained within the local approximation to density-functional theory, and deals with the ground state of metals as obtained from selfconsistent electronic-structure calculations performed by...... metals, and the localization of 3d, 4f, and 5f electrons in the 3d metal monoxides, the light lanthanides, and the actinides, respectively, as well as the cohesive properties of metals in general.!...
Structure of Wet Specimens in Electron Microscopy
Parsons, D. F.
1974-01-01
Discussed are past work and recent advances in the use of electron microscopes for viewing structures immersed in gas and liquid. Improved environmental chambers make it possible to examine wet specimens easily. (Author/RH)
Calculations for electron-impact excitation and ionization of beryllium
Zatsarinny, Oleg; Bartschat, Klaus; Fursa, Dmitry V.; Bray, Igor
2016-12-01
The B-spline R-matrix and the convergent close-coupling methods are used to study electron collisions with neutral beryllium over an energy range from threshold to 100 eV. Coupling to the target continuum significantly affects the results for transitions from the ground state, but to a lesser extent the strong transitions between excited states. Cross sections are presented for selected transitions between low-lying physical bound states of beryllium, as well as for elastic scattering, momentum transfer, and ionization. The present cross sections for transitions from the ground state from the two methods are in excellent agreement with each other, and also with other available results based on nonperturbative convergent pseudostate and time-dependent close-coupling models. The elastic cross section at low energies is dominated by a prominent shape resonance. The ionization from the {(2s2p)}3P and {(2s2p)}1P states strongly depends on the respective term. The current predictions represent an extensive set of electron scattering data for neutral beryllium, which should be sufficient for most modeling applications.
Energy Technology Data Exchange (ETDEWEB)
Hall, B.D. (Inst. de Micro- et Optoelectronique, EPFL, Lausanne (Switzerland)); Reinhard, D. (Inst. de Physique Experimentale, EPFL, Lausanne (Switzerland)); Ugarte, D. (Inst. de Physique Experimentale, EPFL, Lausanne (Switzerland))
1993-05-01
Calculations of the dynamical Debye-Scherrer electron diffraction pattern for ultrafine gold and silver particles have been performed using the multislice method. Two cluster sizes, 31 and 55 A in diameter (923 and 5083 atoms, respectively), of both f.c.c. and icosahedral structures were used, at incident voltages of 40 kV and 100 kV. (orig.)
Geometric and Electronic Structure of Closed Graphene Edges
Energy Technology Data Exchange (ETDEWEB)
Lopez-Benzanilla, Alejandro [Oak Ridge National Laboratory (ORNL); Campos-Delgado, Jessica [IPICyT; Sumpter, Bobby G [ORNL; Baptista, Daniel [National Institute of Metrology, Duque de Caxias, Brazil; Hayashi, Takuya [Institute of Carbon Science and Technology, Shinshu Unversity; Kim, Y A [Shinshu University; Muramatsu, H [Shinshu University; Endo, M [Shinshu University; Achete, Carlos [National Institute of Metrology, Duque de Caxias, Brazil; Terrones, M. [Universidad Carlos III, Madrid, Spain; Meunier, Vincent [ORNL
2012-01-01
We report theoretical and experimental results on single and multiple looped graphene sheets. Experimental images of stable closed-edge structures in few-layer graphene samples obtained by high-resolution transmission electron microscopy (HRTEM) are compared with first- principles density functional theory calculations. We demonstrate that the electronic structure of a graphene nanoribbon is not significantly perturbed upon closing. By contrast, a significant modulation of the electronic structure is observed for closed-edge graphene structures deposited on a planar graphene substrate. This effect is due to an enhanced reactivity of the looped (coalesced) edges observed experimentally. The coexistence of different degrees of curvature in the graphene sheet induced by folding indicates that these materials could be used for surface chemistry engineering.
A nonperturbative calculation of the electron's magnetic moment
Brodsky, S. J.; Franke, V. A.; Hiller, J. R.; McCartor, G.; Paston, S. A.; Prokhvatilov, E. V.
2004-12-01
In principle, the complete spectrum and bound-state wave functions of a quantum field theory can be determined by finding the eigenvalues and eigensolutions of its light-cone Hamiltonian. One of the challenges in obtaining nonperturbative solutions for gauge theories such as QCD using light-cone Hamiltonian methods is to renormalize the theory while preserving Lorentz symmetries and gauge invariance. For example, the truncation of the light-cone Fock space leads to uncompensated ultraviolet divergences. We present two methods for consistently regularizing light-cone-quantized gauge theories in Feynman and light-cone gauges: (1) the introduction of a spectrum of Pauli-Villars fields which produces a finite theory while preserving Lorentz invariance; (2) the augmentation of the gauge-theory Lagrangian with higher derivatives. In the latter case, which is applicable to light-cone gauge ( A=0), the A component of the gauge field is maintained as an independent degree of freedom rather than a constraint. Finite-mass Pauli-Villars regulators can also be used to compensate for neglected higher Fock states. As a test case, we apply these regularization procedures to an approximate nonperturbative computation of the anomalous magnetic moment of the electron in QED as a first attempt to meet Feynman's famous challenge.
Calculations for electron-impact excitation and ionization of beryllium
Zatsarinny, Oleg; Fursa, Dmitry V; Bray, Igor
2016-01-01
The B-spline R-matrix and the convergent close-coupling methods are used to study electron collisions with neutral beryllium over an energy range from threshold to 100 eV. Coupling to the target continuum significantly affects the results for transitions from the ground state, but to a lesser extent the strong transitions between excited states. Cross sections are presented for selected transitions between low-lying physical bound states of beryllium, as well as for elastic scattering, momentum transfer, and ionization. The present cross sections for transitions from the ground state from the two methods are in excellent agreement with each other, and also with other available results based on nonperturbative convergent pseudo-state and time-dependent close-coupling models. The elastic cross section at low energies is dominated by a prominent shape resonance. The ionization from the $(2s2p)^3P$ and $(2s2p)^1P$ states strongly depends on the respective term. The current predictions represent an extensive set o...
DFT calculations of electronic and optical properties of SrS with LDA, GGA and mGGA functionals
Sharma, Shatendra; Sharma, Jyotsna; Sharma, Yogita
2016-05-01
The theoretical investigations of electronic and optical properties of SrS are made using the first principle DFT calculations. The calculations are performed for the local-density approximation (LDA), generalized gradient approximation (GGA) and for an alternative form of GGA i.e. metaGGA for both rock salt type (B1, Fm3m) and cesium chloride (B2, Pm3m) structures. The band structure, density of states and optical spectra are calculated under various available functional. The calculations with LDA and GGA functional underestimate the values of band gaps with all functional, however the values with mGGA show reasonably good agreement with experimental and those calculated by using other methods.
Sarveswari, S.; Srikanth, A.; Arul Murugan, N.; Vijayakumar, V.; Jasinski, Jerry P.; Beauchesne, Hanna C.; Jarvis, Ethan E.
2015-02-01
3E-1-(6-Chloro-2-methyl-4-phenylquinolin-3-yl)-3-arylprop-2-en-1-ones were synthesized and characterized by FTIR, 1H NMR, 13C NMR, HSQC, DEPT-135. In addition the compound 3E-1-(6-chloro-2-methyl-4-phenylquinolin-3-yl)-3-(2,5-dimethoxyphenyl)prop-2-en-1-one was subjected to the single crystal X-ray diffraction studies. Density functional theory calculations were carried out for this chalcone and its derivatives to investigate into their electronic structure, chemical reactivity, linear and non-linear optical properties. The structure predicted from DFT for chalcone is in good agreement with the structure from XRD measurement.
Nishioka, Hirotaka; Ando, Koji
2011-05-28
By making use of an ab initio fragment-based electronic structure method, fragment molecular orbital-linear combination of MOs of the fragments (FMO-LCMO), developed by Tsuneyuki et al. [Chem. Phys. Lett. 476, 104 (2009)], we propose a novel approach to describe long-distance electron transfer (ET) in large system. The FMO-LCMO method produces one-electron Hamiltonian of whole system using the output of the FMO calculation with computational cost much lower than conventional all-electron calculations. Diagonalizing the FMO-LCMO Hamiltonian matrix, the molecular orbitals (MOs) of the whole system can be described by the LCMOs. In our approach, electronic coupling T(DA) of ET is calculated from the energy splitting of the frontier MOs of whole system or perturbation method in terms of the FMO-LCMO Hamiltonian matrix. Moreover, taking into account only the valence MOs of the fragments, we can considerably reduce computational cost to evaluate T(DA). Our approach was tested on four different kinds of model ET systems with non-covalent stacks of methane, non-covalent stacks of benzene, trans-alkanes, and alanine polypeptides as their bridge molecules, respectively. As a result, it reproduced reasonable T(DA) for all cases compared to the reference all-electron calculations. Furthermore, the tunneling pathway at fragment-based resolution was obtained from the tunneling current method with the FMO-LCMO Hamiltonian matrix.
Ab Initio Calculations for the BaTiO3 (001) Surface Structure
Institute of Scientific and Technical Information of China (English)
XUE Xu-Yan; WANG Chun-Lei; ZHONG Wei-Lie
2004-01-01
@@ The ab initio method within the local density approximation is applied to calculate cubic BaTiO3 (001) surface relaxation and rumpling for two different terminations (BaO and TiO2). Our calculations demonstrate that cubic perovskite BaTiO3 crystals possess surface polarization, accompanied by the presence of the relevant electric field.We analyse their electronic structures (band structure, density of states and the electronic density redistribution with emphasis on the covalency effects). The results are also compared with that of the previous ab initio calculations. Considerable increases of Ti-O chemical bond covalency nearby the surface have been observed.The band gap reduces especially for the TiO2 termination.
Calculation of surface acoustic waves in a multilayered piezoelectric structure
Institute of Scientific and Technical Information of China (English)
Zhang Zuwei; Wen Zhiyu; Hu Jing
2013-01-01
The propagation properties of the surface acoustic waves (SAWs) in a ZnO-SiO2-Si multilayered piezoelectric structure are calculated by using the recursive asymptotic method.The phase velocities and the electromechanical coupling coefficients for the Rayleigh wave and the Love wave in the different ZnO-SiO2-Si structures are calculated and analyzed.The Love mode wave is found to be predominantly generated since the c-axis of the ZnO film is generally perpendicular to the substrate.In order to prove the calculated results,a Love mode SAW device based on the ZnO-SiO2-Si multilayered structure is fabricated by micromachining,and its frequency responses are detected.The experimental results are found to be mainly consistent with the calculated ones,except for the slightly larger velocities induced by the residual stresses produced in the fabrication process of the films.The deviation of the experimental results from the calculated ones is reduced by thermal annealing.
Amberger, Hanns-Dieter; Reddmann, Hauke; Mueller, Thomas J; Evans, William J
2014-10-15
The polarized Raman spectra of an oriented La(η(5)-C5Me5)3 (1) single crystal (where the principal axes of the two molecules per unit cell are uniformly oriented) as well as the mid (ca. 90K) and far infrared spectra of pellets have been recorded. Applying the selection rules of C3h symmetry to the spectra obtained, the irreducible representations (irreps) of numerous lines/bands of intra-ligand character were derived. In the range theory (DFT) were performed. In the intra-ligand range >400cm(-1), the obtained results agree well with the experimental findings. Because of the strong mixing at lower wavenumbers, even the separation of calculated skeletal and intra-ligand modes and the identification of the former was only successful by comparing the calculated FIR and averaged Raman spectra of compound 1 with those of La(η(5)-C5Me4H)3 (2). Making use of both the calculated frequencies of normal modes and their polarizability tensors, the polarized Raman spectra of an oriented single crystal of 1 in the range <400cm(-1) were calculated and compared to the experimental ones. Because of an overestimation of the mixing of normal vibrations of A' symmetry, the experimental intensities of the lines of the symmetric stretch ν1(A') were not reproduced by the calculation for compound 1 but by that for Sm(η(5)-C5Me5)3 (3). Skeletal and intra-ligand modes were separated and designated. Neglecting νC-H modes, the DFT calculation for 1 achieved an r.m.s. deviation of 17.9cm(-1) for 72 assignments.
Electronic structures and properties of Ti, Zr and Hf metals
Institute of Scientific and Technical Information of China (English)
无
2001-01-01
The electronic structures of pure Ti, Zr and Hf metals with hcp structure were determined by one-atom (OA) theory. According to the electronic structures of these metals,their potential curves, cohesive energies, lattice constants, elasticities and the temperature dependence of linear thermal expansion coefficients were calculated. The electronic structures and characteristic properties of these metals with bcc and fcc structures and liquids were also studied. The results show that the electronic structures of Ti, Zr and Hf metals are respectively [Ar](3dn)0.481 0(3dc)2.085 7(4sc)1.000 0(4sf)0.433 3, [Kr](4dn)0.396 8(4dc)2.142 8(5sc)1.262 0(5sf)0.198 4, [Xe](5dn)0.368 0(5dc)2.041 4(6sc)1.406 6(6sf)0.184 0. It is explained why the pure Ti, Zr and Hf metals with hcp and bcc structures can exist naturally, while those with fcc structure can not.
Calculation of IR-spectra of structural fragments of lignins
Derkacheva, O. Yu.; Ishankhodzhaeva, M. M.
2016-12-01
To study structure of softwood lignins the experimental and theoretical IR-spectra in middle IR-diapason were analyzed. To interpret these data the quantum chemical calculations of IR-spectra of general dimmer fragments of softwood lignins by method of density functional theory (DFT/B3LYP) with 6-31G(d,p) as basis set were carried out. These calculations showed that frequencies of normal vibrations of fragment with β-alkyl-aryl linkage are close to the experimental values of the IR absorption bands of lignin, and infrared spectrum of this structure is similar to the experimental spectrum of lignin. The calculations with accounting for the solvent showed a strong increase in the intensity of the majority of the bands and the solvent effect on the frequencies of vibrations.
Iitaka, T.; Nomura, S.; Hirayama, H.; Zhao, X. W.; Aoyagi, Y.; Sugano, T.
1997-08-01
We introduce a new linear scaling( ( O(N) ) ) algorithm [1] for calculating linear response functions of non-interacting electrons. It requires only ( O(N) ) computational efforts where ( N ) is the dimension of the statevector, because it avoids ( O(N^3) ) computational effort for calculating large number of eigenstates, i.e., the occupied one-electron states up to the Fermi energy and the unoccupied states with higher energy. The advantage of this method compared to the Chebyshev polynomial method recently developed by Wang [2] is that it does not need any storage of huge statevectors on hard disks. The application of this method to photonic band structures [3], and silicon nanocrystalites [3,4] will be also presented. [ 1 ] T. Iitaka, S. Nomura, H. Hirayama, X.W. Zhao, Y. Aoyagi, T. Sugano, to appear in Phys. Rev. E, preprint is available at xxx.lanl.gov/abs/cond-mat/9703224>cond- mat/9703224. See also http://espero.riken.go.jp/. [ 2 ] L.W. Wang, Phys. Rev. B 49, 10154 (1994); L.W. Wang, Phys. Rev. Lett. 73, 1039 (1994) . [ 3 ] H. Hirayama et al., S. Nomura et al., and T. Iitaka et al., in LDSD97, Lisbon, Portugal 19-20 May 1997. The proceedings will appear in Materials Science & Engineering B. [ 4 ] S. Nomura et al., (submitted to Phys. Rev. B).
Structural uncertainty in air mass factor calculation for NO
Lorente Delgado, Alba; Folkert Boersma, K.; Yu, Huan; Dörner, Steffen; Hilboll, Andreas; Richter, Andreas; Liu, Mengyao; Lamsal, Lok N.; Barkley, Michael; Smedt, De Isabelle; Roozendael, Van Michel; Wang, Yang; Wagner, Thomas; Beirle, Steffen; Lin, Jin Tai; Krotkov, Nickolay; Stammes, Piet; Wang, Ping; Eskes, Henk J.; Krol, Maarten
2017-01-01
Air mass factor (AMF) calculation is the largest source of uncertainty in NO2 and HCHO satellite retrievals in situations with enhanced trace gas concentrations in the lower troposphere. Structural uncertainty arises when different retrieval methodologies are applied within the scientific community
Quantum mechanical computation of structural, electronic, and thermoelectric properties of AgSbSe2
Directory of Open Access Journals (Sweden)
M Salimi
2015-07-01
Full Text Available In this work, density functional calculations and Boltzmann semiclassical theory of transport are used to investigate structural, electronic, and thermoelectric properties of AgSbSe2 crystal. According to the published experimental measurements, five more likely structures of this compound are considered and their structural and electronic properties are calculated and compared together. Then, thermoelectric properties (electrical conductivity, electronic contribution to the thermal conductivity, power factor, and Seebeck coefficient of three more stable structures are investigated in the constant relaxation time approximation. Finally, the calculated temperature dependence of Seebeck coefficient is compared with the corresponding experimental measurements of others.
Yamada, Shunsuke; Akashi, Ryosuke; Tsuneyuki, Shinji
2016-01-01
We present an efficient post-processing method for calculating the electronic structure of nanosystems based on the divide-and-conquer approach to density functional theory (DC-DFT), in which a system is divided into subsystems whose electronic structure is solved separately. In this post process, the Kohn-Sham Hamiltonian of the total system is easily derived from the orbitals and orbital energies of subsystems obtained by DC-DFT without time-consuming and redundant computation. The resultant orbitals spatially extended over the total system are described as linear combinations of the orbitals of the subsystems. The size of the Hamiltonian matrix can be much reduced from that for conventional calculation, so that our method is fast and applicable to general huge systems for investigating the nature of electronic states.
Yamada, Shunsuke; Shimojo, Fuyuki; Akashi, Ryosuke; Tsuneyuki, Shinji
2017-01-01
We present an efficient postprocessing method for calculating the electronic structure of nanosystems based on the divide-and-conquer approach to density functional theory (DC-DFT), in which a system is divided into subsystems whose electronic structure is solved separately. In this postprocess, the Kohn-Sham Hamiltonian of the total system is easily derived from the orbitals and orbital energies of subsystems obtained by DC-DFT without time-consuming and redundant computation. The resultant orbitals spatially extended over the total system are described as linear combinations of the orbitals of the subsystems. The size of the Hamiltonian matrix can be much reduced from that for the conventional calculation, so our method is fast and applicable to general huge systems for investigating the nature of electronic states.
Prosenc, Marc Heinrich; Reddmann, Hauke; Amberger, Hanns-Dieter
2012-02-15
Previous empirical assignments of the normal modes of Ru(η(5)-C(5)H(5))(2) were checked against the results of a calculation applying density functional theory (DFT). After some reassignments, following those recently suggested for Fe(η(5)-C(5)H(5))(2) (after theoretical model calculations), a satisfactory agreement was observed. Recently communicated polarized Raman spectra of an oriented Ru(η(5)-C(5)Me(5))(2) single crystal were used here for the identification of the irreducible representations of a number of Raman active normal modes (assuming molecular D(5h) symmetry) which agree well with the results of the DFT calculation. The energies of IR active fundamental vibrations, extracted from recently communicated FIR/MIR spectra (pellets), were correlated with comparable energies of IR allowed irreducible representations of the DFT calculation and assigned. Both the skeletal and the intra-ligand normal modes could be correlated with the idealized standard motions (ν(i)s) of the model sandwich complex Ru(C(5)C(5))(2), and previous assignments had to be revised. Neglecting the νCH vibrations (which are off by ca. 50cm(-1)) an r.m.s. deviation of 9.8cm(-1) (for 47 assignments) of the remaining normal modes could be achieved.
Structural and electronic properties of carbon nanotubes under hydrostatic pressures
Institute of Scientific and Technical Information of China (English)
Zhang Ying; Cao Jue-Xian; Yang Wei
2008-01-01
We studied the structural and electronic properties of carbon nanotubes under hydrostatic pressures based on molecular dynamics simulations and first principles band structure calculations.It is found that carbon nanotubes experience a hard-to-soft transition as external pressure increases.The bulk modulus of soft phase is two orders of magnitude smaller than that of hard phase.The band structure calculations show that band gap of (10,0) nanotube increases with the increase of pressure at low pressures. Above a critical pressure (5.70GPa),band gap of (10,0) nanotube drops rapidly and becomes zero at 6.62GPa. Moreover,the calculated charge density shows that a large pressure can induce an sp2-to-sp3 bonding transition,which is confirmed by recent experiments on deformed carbon nanotubes.
The electronic structure of NiAl and NiSi
Sarma, D. D.; Speier, W.; Zeller, R.; Leuken, E. van; Groot, R.A. de; Fuggle, J.C.
1989-01-01
A study of the electronic structures of NiSi and NiAl employing electron spectroscopies and theoretical calculations is presented. Experimental results, obtained with x-ray photoemission and bremsstrahlung isochromat spectroscopy, are interpreted by means of density of states and matrix element calculations for the compounds in their real crystal structure. This gives a detailed picture of the electronic states over the whole bonding-anti-bonding region below and above the Fermi level. Cluste...
All-electron versus pseudopotential calculation of optical properties: the case of GaAs
Energy Technology Data Exchange (ETDEWEB)
Monachesi, P.; Marini, A.; Onida, G.; Palummo, M.; Sole, R. del [Tor Vergata Univ., Rome (Italy). Dipt. di Fisica
2001-03-16
The reliability of the widespread practice of calculating the optical properties of solids using pseudo wavefunctions instead of the true electron wavefunctions has been tested in the case of bulk GaAs. Pseudopotential calculations of the imaginary part of the dielectric function - where the matrix elements of the momentum operator are calculated between pseudo wavefunctions - have been compared with all-electron full-potential linear muffin-tin orbital calculations where the true wavefunctions are used. No evidence has been found of differences due to the different sets of wavefunctions employed in the two approaches. (orig.)
Electronic structure and superconductivity of MgB2
Indian Academy of Sciences (India)
D M Gaitonde; P Modak; R S Rao; B K Godwal
2003-01-01
Results of ab initio electronic structure calculations on the compound, MgB2, using the FPLAPW method employing GGA for the exchange–correlation energy are presented. Total energy minimization enables us to estimate the equilibrium volume, / ratio and the bulk modulus, all of which are in excellent agreement with experiment. We obtain the mass enhancement parameter by using our calculated, $D(E_F)$ and the experimental specific heat data. The $T_c$ is found to be 37 K. We use a parametrized description of the calculated band structure to obtain the = 0 K values of the London penetration depth and the superconducting coherence length. The penetration depth calculated by us is too small and the coherence length too large as compared to the experimentally determined values of these quantities. This indicates the limitations of a theory that relies only on electronic structure calculations in describing the superconducting state in this material and implies that impurity effects as well as mass renormalization effects need to be included.
Electronic structure of the radical-cations of phenothiazine and its structural analogs
Energy Technology Data Exchange (ETDEWEB)
Turchaninov, V.K.; Ermikov, A.F.; Shagun, V.A.
1986-09-20
The electronic structure of the radical-cations of phenothiazine and some of its derivatives and heteroanalogs was investigated by electronic absorption spectroscopy. On the basis of the obtained results and also of the data from photoelectron spectroscopy of the parent molecules, quantum-chemical calculations (MINDO/3), and published data it was concluded that the occupied molecular orbitals of the excess-..pi.. heteroatomic system exhibit different sensitivities to hole formation. It is suggested that this is due to the different degrees of delocalization of the unpaired electron in the ground and electronically excited states of the radical cation of such molecules.
Chiral nucleon-nucleon forces in nuclear structure calculations
Directory of Open Access Journals (Sweden)
Coraggio L.
2016-01-01
Full Text Available Realistic nuclear potentials, derived within chiral perturbation theory, are a major breakthrough in modern nuclear structure theory, since they provide a direct link between nuclear physics and its underlying theory, namely the QCD. As a matter of fact, chiral potentials are tailored on the low-energy regime of nuclear structure physics, and chiral perturbation theory provides on the same footing two-nucleon forces as well as many-body ones. This feature fits well with modern advances in ab-initio methods and realistic shell-model. Here, we will review recent nuclear structure calculations, based on realistic chiral potentials, for both finite nuclei and infinite nuclear matter.
Oberhofer, Harald; Blumberger, Jochen
2010-12-01
We present a plane wave basis set implementation for the calculation of electronic coupling matrix elements of electron transfer reactions within the framework of constrained density functional theory (CDFT). Following the work of Wu and Van Voorhis [J. Chem. Phys. 125, 164105 (2006)], the diabatic wavefunctions are approximated by the Kohn-Sham determinants obtained from CDFT calculations, and the coupling matrix element calculated by an efficient integration scheme. Our results for intermolecular electron transfer in small systems agree very well with high-level ab initio calculations based on generalized Mulliken-Hush theory, and with previous local basis set CDFT calculations. The effect of thermal fluctuations on the coupling matrix element is demonstrated for intramolecular electron transfer in the tetrathiafulvalene-diquinone (Q-TTF-Q-) anion. Sampling the electronic coupling along density functional based molecular dynamics trajectories, we find that thermal fluctuations, in particular the slow bending motion of the molecule, can lead to changes in the instantaneous electron transfer rate by more than an order of magnitude. The thermal average, ( { } )^{1/2} = 6.7 {mH}, is significantly higher than the value obtained for the minimum energy structure, | {H_ab } | = 3.8 {mH}. While CDFT in combination with generalized gradient approximation (GGA) functionals describes the intermolecular electron transfer in the studied systems well, exact exchange is required for Q-TTF-Q- in order to obtain coupling matrix elements in agreement with experiment (3.9 mH). The implementation presented opens up the possibility to compute electronic coupling matrix elements for extended systems where donor, acceptor, and the environment are treated at the quantum mechanical (QM) level.
Effects of NMR spectral resolution on protein structure calculation.
Directory of Open Access Journals (Sweden)
Suhas Tikole
Full Text Available Adequate digital resolution and signal sensitivity are two critical factors for protein structure determinations by solution NMR spectroscopy. The prime objective for obtaining high digital resolution is to resolve peak overlap, especially in NOESY spectra with thousands of signals where the signal analysis needs to be performed on a large scale. Achieving maximum digital resolution is usually limited by the practically available measurement time. We developed a method utilizing non-uniform sampling for balancing digital resolution and signal sensitivity, and performed a large-scale analysis of the effect of the digital resolution on the accuracy of the resulting protein structures. Structure calculations were performed as a function of digital resolution for about 400 proteins with molecular sizes ranging between 5 and 33 kDa. The structural accuracy was assessed by atomic coordinate RMSD values from the reference structures of the proteins. In addition, we monitored also the number of assigned NOESY cross peaks, the average signal sensitivity, and the chemical shift spectral overlap. We show that high resolution is equally important for proteins of every molecular size. The chemical shift spectral overlap depends strongly on the corresponding spectral digital resolution. Thus, knowing the extent of overlap can be a predictor of the resulting structural accuracy. Our results show that for every molecular size a minimal digital resolution, corresponding to the natural linewidth, needs to be achieved for obtaining the highest accuracy possible for the given protein size using state-of-the-art automated NOESY assignment and structure calculation methods.
Electronic structures and optical properties of two anthracene derivatives
Institute of Scientific and Technical Information of China (English)
ZHANG Peng; XIA Baohui; SUN Yinghui; YANG Bing; TIAN Wenjing; WANG Yue; ZHANG Guo
2006-01-01
The electronic structures and the optical properties of two anthracene derivatives, DBMA and DAA, are investigated by both experimental techniques and quantum chemical calculations. The cyclic voltammetry and differential pulse polarograph measurement revealed that the introduction of benzol-imidazol and pyrrolo-pyridine group on the anthracene block can affect the electrochemical behavior of DBMA and DAA. Both UV/visible absorption and emission spectra of DBMA and DAA are red-shifted in contrast to the unsubstituted anthracene, so that the anthracene derivatives emit at blue-green region and the luminescence yields are remarkably elevated (over 90%). The B3LYP/6-31G theoretical calculations explored that the electronic structures of the anthracene derivatives are perturbed by the side substitutes on the anthracene block, and the slight variation of the electronic structures results in the enhanced electron accepting ability and the decrease of the HOMO-LUMO energy gap,which is the origin of the emission to be shifted to blue-green region. The non-planar geometry structures of DBMA and DAA are responsible for the excellent luminescence yields.
Electronic Structure of Gadolinium Calcium Oxoborate
Energy Technology Data Exchange (ETDEWEB)
Nelson, A; Adams, J; Schaffers, K
2004-07-01
Gadolinium calcium oxoborate (GdCOB) is a nonlinear optical material that belongs to the calcium--rare-earth (R) oxoborate family, with general composition Ca{sub 4}RO(BO{sub 3}){sub 3} (R{sup 3+} = La, Sm, Gd, Lu, Y). X-ray photoemission was applied to study the valence band electronic structure and surface chemistry of this material. High resolution photoemission measurements on the valence band electronic structure and Gd 3d and 4d, Ca 2p, B 1s and O 1s core lines were used to evaluate the surface and near surface chemistry. These results provide measurements of the valence band electronic structure and surface chemistry of this rare-earth oxoborate.
Structural and electronic properties of arsenic nitrogen monolayer
Liu, Pei; Nie, Yao-zhuang; Xia, Qing-lin; Guo, Guang-hua
2017-03-01
We present our first-principles calculations of a new two-dimensional material, arsenic nitrogen monolayer. The structural, electronic, and mechanical properties are investigated in detail by means of density functional theory computations. The calculated binding energy and the phonon spectra demonstrate that the AsN can form stable monolayer in puckered honeycomb structure. It is a semiconductor with indirect band gap of 0.73 eV, and displays highly anisotropic mechanical properties. Strain has obvious influence on the electronic properties of AsN monolayer. It is found that in the armchair direction, a moderate compression strain (-12%) can trigger an indirect to direct band gap transition and a tensile strain of 18% can make the AsN becoming a stable metal. In the zigzag direction, a rather smaller strain than armchair direction (12% for compression and 8% for stretch) can induce the indirect band gap to metal transition.
Band Structure and Optical Properties of Kesterite Type Compounds: first principle calculations
Palaz, S.; Unver, H.; Ugur, G.; Mamedov, A. M.; Ozbay, E.
2017-02-01
In present work, our research is mainly focused on the electronic structures, optical and magnetic properties of Cu2FeSnZ4 (Z = S, Se) compounds by using ab initio calculations within the generalized gradient approximation (GGA). The calculations are performed by using the Vienna ab-initio simulation package (VASP) based on the density functional theory. The band structure of the Cu2FeSnZ4 ( Z = S, Se) compounds for majority spin (spin-up) and minority spin (spin-down) were calculated. It is seen that for these compounds, the majority spin states cross the Fermi level and thus have the metallic character, while the minority spin states open the band gaps around the Fermi level and thus have the narrow-band semiconducting nature. For better understanding of the electronic states, the total and partial density of states were calculated, too. The real and imaginary parts of dielectric functions and hence the optical functions such as energy-loss function, the effective number of valance electrons and the effective optical dielectric constant for Cu2FeSnZ4 (Z = S, Se) compounds were also calculated.
Shao, Yongliang; Zhang, Lei; Hao, Xiaopeng; Wu, Yongzhong; Dai, Yuanbin; Tian, Yuan; Huo, Qin
2014-08-05
We report a method to obtain the stress of crystalline materials directly from lattice deformation by Hooke's law. The lattice deformation was calculated using the crystallographic orientations obtained from electron backscatter diffraction (EBSD) technology. The stress distribution over a large area was obtained efficiently and accurately using this method. Wurtzite structure gallium nitride (GaN) crystal was used as the example of a hexagonal crystal system. With this method, the stress distribution of a GaN crystal was obtained. Raman spectroscopy was used to verify the stress distribution. The cause of the stress distribution found in the GaN crystal was discussed from theoretical analysis and EBSD data. Other properties related to lattice deformation, such as piezoelectricity, can also be analyzed by this novel approach based on EBSD data.
Heat Transfer Principles in Thermal Calculation of Structures in Fire.
Zhang, Chao; Usmani, Asif
2015-11-01
Structural fire engineering (SFE) is a relatively new interdisciplinary subject, which requires a comprehensive knowledge of heat transfer, fire dynamics and structural analysis. It is predominantly the community of structural engineers who currently carry out most of the structural fire engineering research and design work. The structural engineering curriculum in universities and colleges do not usually include courses in heat transfer and fire dynamics. In some institutions of higher education, there are graduate courses for fire resistant design which focus on the design approaches in codes. As a result, structural engineers who are responsible for structural fire safety and are competent to do their jobs by following the rules specified in prescriptive codes may find it difficult to move toward performance-based fire safety design which requires a deep understanding of both fire and heat. Fire safety engineers, on the other hand, are usually focused on fire development and smoke control, and may not be familiar with the heat transfer principles used in structural fire analysis, or structural failure analysis. This paper discusses the fundamental heat transfer principles in thermal calculation of structures in fire, which might serve as an educational guide for students, engineers and researchers. Insights on problems which are commonly ignored in performance based fire safety design are also presented.
Institute of Scientific and Technical Information of China (English)
H. Koc; A. Yildirim; E. Deligoz
2012-01-01
The structural,elastic,electronic,optical,and vibrational properties of cubic PdGa compound are investigated using the norm-conserving pseudopotentials within the local density approximation (LDA) in the framework of the density functional theory.The calculated lattice constant has been compared with the experimental value and has been found to be in good agreement with experimental data.The obtained electronic band structures show that PdGa compound has no band gap.The second-order elastic constants have been calculated,and the other related quantities such as the Young's modulus,shear modulus,Poisson's ratio,anisotropy factor,sound velocities,and Debye temperature have also been estimated.Our calculated results of elastic constants show that this compound is mechanically stable.Furthermore,the real and imaginary parts of the dielectric function and the optical constants such as the electron energy-loss function,the optical dielectric constant and the effective number of electrons per unit cell are calculated and presented in the study.The phonon dispersion curves are also derived using the direct method.
Calculation of Gas and Electronic Temperatures in the Channel of the Direct Current Arc
Gerasimov, Alexander V.; Kirpichnikov, Alexander P.
2009-10-01
The results of calculations of gas and electronic temperatures in the channel of an arc plasma generator are presented. The calculations were carried out within the framework of a self-consistent two-temperature channel model of an arc discharge. The given method can be used with good precision to determine the radial distribution of gas and electronic temperatures in conducting and non-conducting zones of a constant current arc at designated parameters of the discharge (current intensity and power).
Ramalingam, S; Jayaprakash, A; Mohan, S; Karabacak, M
2011-11-01
FT-IR and FT-Raman (4000-100 cm(-1)) spectral measurements of 3-methyl-1,2-butadiene (3M12B) have been attempted in the present work. Ab-initio HF and DFT (LSDA/B3LYP/B3PW91) calculations have been performed giving energies, optimized structures, harmonic vibrational frequencies, IR intensities and Raman activities. Complete vibrational assignments on the observed spectra are made with vibrational frequencies obtained by HF and DFT (LSDA/B3LYP/B3PW91) at 6-31G(d,p) and 6-311G(d,p) basis sets. The results of the calculations have been used to simulate IR and Raman spectra for the molecule that showed good agreement with the observed spectra. The potential energy distribution (PED) corresponding to each of the observed frequencies are calculated which confirms the reliability and precision of the assignment and analysis of the vibrational fundamentals modes. The oscillation of vibrational frequencies of butadiene due to the couple of methyl group is also discussed. A study on the electronic properties such as HOMO and LUMO energies, were performed by time-dependent DFT (TD-DFT) approach. The calculated HOMO and LUMO energies show that charge transfer occurs within the molecule. The thermodynamic properties of the title compound at different temperatures reveal the correlations between standard heat capacities (C) standard entropies (S), and standard enthalpy changes (H).
Institute of Scientific and Technical Information of China (English)
陈琦丽; 唐超群
2009-01-01
采用密度泛函理论(DFT)平面波赝势方法计算了N/F掺杂和N-F双掺杂锐钛矿相TiO2(101)表面的电子结构.由于DFT方法存在对过渡金属氧化物带隙能的计算结果总是与实际值严重偏离的缺陷,本文也采用DFT+U(Hubbard系数)方法对模型的电子结构进行了计算.DFT的计算结果表明N掺杂后,N2p轨道与O 2p和Ti 3d价带轨道的混合会导致TiO2带隙能的降低,而F掺杂以及氧空位的引入对材料的电子结构没有明显的影响.DFT+U的计算却给出截然不间的结果,N掺杂并没有导致带隙能的降低,而只是在带隙中引入一个孤立的杂质能级,反而F掺杂以及氧空位的引入带来明显的带隙能降低.DFT+U的计算结果与一些实验测量结果能够较好地符合.%Electronic structures of nitrogen(N)/fluorine(F)-doped and N-F-codoped TiO2 anatase(101)surfaces were investigated by density functional theory(DFT)plane-wave pseudopotential method.Since DFT calculations performed on transition metal oxides always lead to a severe underestimation of the band gap,DFT+U(Hubbard coefficient)method was also adopted to calculate the electronic structures.DFT results demonstrated that mixing of N 2p states with O 2p and Ti 3d valence band(VB)states contributes to the band gap reduction of TiO2 whereas F doping and the introduction of oxygen vacancies have no obvious effect on the electronic structure.However,from DFT+U,no obvious band gap narrowing was observed by N-doping except for the isolated N 2p states lying in the gap.In DFT+U calculation,F-doping as well as the introduction of oxygen vacancies leads to an obvious band gap narrowing.Results from DFT+U calculations accord well with some experimental results.
Electronic structure and magnetism in actinide compounds
Energy Technology Data Exchange (ETDEWEB)
Durakiewicz, T. [Los Alamos National Laboratory, Los Alamos, NM 87545 (United States)]. E-mail: tomasz@lanl.gov; Joyce, J.J. [Los Alamos National Laboratory, Los Alamos, NM 87545 (United States); Lander, G.H. [JRC, Institute of Transuranium Elements, Postfach 2340, 76125 Karlsruhe (Germany); Olson, C.G. [Ames Laboratory, Iowa State University, Ames, Iowa 5011 (United States); Butterfield, M.T. [Lawrence Livermoore National Laboratory, Livermoore, CA 94550 (United States); Guziewicz, E. [Institute of Physics, Polish Academy of Sciences, 02-668 Warsaw (Poland); Batista, C.D. [Los Alamos National Laboratory, Los Alamos, NM 87545 (United States); Arko, A.J. [Los Alamos National Laboratory, Los Alamos, NM 87545 (United States); Morales, L. [Los Alamos National Laboratory, Los Alamos, NM 87545 (United States); Mattenberger, K. [Laboratorium fur Festkorperphysik, ETH, CH-8093, Zurich (Switzerland); Vogt, O. [Laboratorium fur Festkorperphysik, ETH, CH-8093, Zurich (Switzerland)
2006-05-01
A close relationship between electronic structure and magnetic properties is observed in actinide compounds. The exact nature of this relationship is under investigation. We present examples of a direct link between electronic structure and ordered magnetic moment and/or magnetization. Specifically, results obtained for cubic U, Np and Pu compounds and quasi-2D U compounds are be presented. In the case of cubic compounds, a direct relationship between binding energy of valence band features and magnetic moment will be discussed. A Stoner-like mechanism and simple mean-field explanation is proposed for ferromagnetic UTe.
Critical analysis of fragment-orbital DFT schemes for the calculation of electronic coupling values
Energy Technology Data Exchange (ETDEWEB)
Schober, Christoph; Reuter, Karsten; Oberhofer, Harald, E-mail: harald.oberhofer@ch.tum.de [Chair for Theoretical Chemistry, Technische Universität München, Lichtenbergstr. 4, D-85747 Garching (Germany)
2016-02-07
We present a critical analysis of the popular fragment-orbital density-functional theory (FO-DFT) scheme for the calculation of electronic coupling values. We discuss the characteristics of different possible formulations or “flavors” of the scheme which differ by the number of electrons in the calculation of the fragments and the construction of the Hamiltonian. In addition to two previously described variants based on neutral fragments, we present a third version taking a different route to the approximate diabatic state by explicitly considering charged fragments. In applying these FO-DFT flavors to the two molecular test sets HAB7 (electron transfer) and HAB11 (hole transfer), we find that our new scheme gives improved electronic couplings for HAB7 (−6.2% decrease in mean relative signed error) and greatly improved electronic couplings for HAB11 (−15.3% decrease in mean relative signed error). A systematic investigation of the influence of exact exchange on the electronic coupling values shows that the use of hybrid functionals in FO-DFT calculations improves the electronic couplings, giving values close to or even better than more sophisticated constrained DFT calculations. Comparing the accuracy and computational cost of each variant, we devise simple rules to choose the best possible flavor depending on the task. For accuracy, our new scheme with charged-fragment calculations performs best, while numerically more efficient at reasonable accuracy is the variant with neutral fragments.
Critical analysis of fragment-orbital DFT schemes for the calculation of electronic coupling values.
Schober, Christoph; Reuter, Karsten; Oberhofer, Harald
2016-02-07
We present a critical analysis of the popular fragment-orbital density-functional theory (FO-DFT) scheme for the calculation of electronic coupling values. We discuss the characteristics of different possible formulations or "flavors" of the scheme which differ by the number of electrons in the calculation of the fragments and the construction of the Hamiltonian. In addition to two previously described variants based on neutral fragments, we present a third version taking a different route to the approximate diabatic state by explicitly considering charged fragments. In applying these FO-DFT flavors to the two molecular test sets HAB7 (electron transfer) and HAB11 (hole transfer), we find that our new scheme gives improved electronic couplings for HAB7 (-6.2% decrease in mean relative signed error) and greatly improved electronic couplings for HAB11 (-15.3% decrease in mean relative signed error). A systematic investigation of the influence of exact exchange on the electronic coupling values shows that the use of hybrid functionals in FO-DFT calculations improves the electronic couplings, giving values close to or even better than more sophisticated constrained DFT calculations. Comparing the accuracy and computational cost of each variant, we devise simple rules to choose the best possible flavor depending on the task. For accuracy, our new scheme with charged-fragment calculations performs best, while numerically more efficient at reasonable accuracy is the variant with neutral fragments.
Structural Features That Stabilize ZnO Clusters: An Electronic Structure Approach
Directory of Open Access Journals (Sweden)
Csaba E. Szakacs
2013-05-01
Full Text Available We show that a simple approach to building small computationally inexpensive clusters offers insights on specific structural motifs that stabilize the electronic structure of ZnO. All-electron calculations on ZniOi needle (i = 6, 9, 12, 15, and 18 and plate (i = 9 and 18 clusters within the density functional theory (DFT formalism show a higher stability for ZnO needles that increases with length. Puckering of the rings to achieve a more wurtzite-like structure destabilizes the needles, although this destabilization is reduced by going to infinite needles (calculated using periodic boundary conditions. Calculations of density of states (DOS curves and band gaps for finite clusters and infinite needles highlight opportunities for band-gap tuning through kinetic control of nanocrystal growth.
Electronic States in Quasi-one-Dimensional Copolymeric Sandwich Structures
Institute of Scientific and Technical Information of China (English)
刘德胜; 王鹿霞; 魏建华; 郑斌; 解士杰; 韩圣浩; 梅良模
2001-01-01
The electronic properties of xPA/nPPP/yPA sandwiched copo]ymers with a well-barrier-well structure have been studied by using a tight-binding calculation. It was found that the electronic properties of the neutral states of these sandwiched copolymers are sensitive to the constitutions of PPP and PA monomers and the interface coupling between PA and PPP. It is verified that the quantum tunnelling effect will occur at the lowest conductive state of xPA/nPPP/xPA copolymers.
Electronic structure of EuN: Growth, spectroscopy, and theory
DEFF Research Database (Denmark)
Richter, J. H.; Ruck, B.J.; Simpson, M.
2011-01-01
We present a detailed study of the electronic structure of europium nitride (EuN), comparing spectroscopic data to the results of advanced electronic structure calculations. We demonstrate the epitaxial growth of EuN films, and show that in contrast to other rare-earth nitrides successful growth...... and the lowest-lying 8S multiplet. The Hubbard-I model is also in good agreement with purely atomic multiplet calculations for the Eu M-edge XAS. LSDA+U and DMFT calculations find a metallic ground state, while QSGW results predict a direct band gap at X for EuN of about 0.9 eV that matches closely an absorption...... edge seen in optical transmittance at 0.9 eV, and a smaller indirect gap. Overall, the combination of theoretical methods and spectroscopies provides insights into the complex nature of the electronic structure of this material. The results imply that EuN is a narrow-band-gap semiconductor that lies...
Can Coulomb Sturmians Be Used as a Basis for N-Electron Molecular Calculations?
DEFF Research Database (Denmark)
Avery, John Scales; Avery, James Emil
2009-01-01
A method is proposed for using isoenergetic configurations formed from many-center Coulomb Sturmians as a basis for calculations on N-electron molecules. Such configurations are solutions to an approximate N-electron Schrödinger equation with a weighted potential, and they are thus closely analog...
Energy Technology Data Exchange (ETDEWEB)
Fujimoto, Kazuhiro J., E-mail: fujimoto@ruby.kobe-u.ac.jp [Department of Computational Science, Graduate School of System Informatics, Kobe University, 1-1, Rokkodai, Nada, Kobe 657-8501 (Japan)
2014-12-07
A transition charge, dipole, and quadrupole from electrostatic potential (TrESP-CDQ) method for electronic coupling calculations is proposed. The TrESP method is based on the classical description of electronic Coulomb interaction between transition densities for individual molecules. In the original TrESP method, only the transition charge interactions were considered as the electronic coupling. In the present study, the TrESP method is extended to include the contributions from the transition dipoles and quadrupoles as well as the transition charges. Hence, the self-consistent transition density is employed in the ESP fitting procedure. To check the accuracy of the present approach, several test calculations are performed to a helium dimer, a methane dimer, and an ethylene dimer. As a result, the TrESP-CDQ method gives a much improved description of the electronic coupling, compared with the original TrESP method. The calculated results also show that the self-consistent treatment to the transition densities contributes significantly to the accuracy of the electronic coupling calculations. Based on the successful description of the electronic coupling, the contributions to the electronic coupling are also analyzed. This analysis clearly shows a negligible contribution of the transition charge interaction to the electronic coupling. Hence, the distribution of the transition density is found to strongly influence the magnitudes of the transition charges, dipoles, and quadrupoles. The present approach is useful for analyzing and understanding the mechanism of excitation-energy transfer.
Calculation of two-center one-electron molecular integrals with STOs. [BICEN
Energy Technology Data Exchange (ETDEWEB)
Rico, J.F.; Lopez, R.; Paniagua, M.; Ramirez, G. (Universidad Autonoma de Madrid (Spain). Dept. de Quimica Fisica y Quimica Cuantica)
1991-05-01
A program for the calculation of two-center one-electron integrals (overlap, nuclear attraction and kinetic energy) between real Slater-type orbitals (STOs) is reported. The integrals are obtained by recursion over simple auxiliary matrices, whose elements are calculated in terms of further auxiliary functions evaluated in a quick and accurate way. (orig.).